Rotating hydraulic machine equipped with pistons

Abstract

The hydraulic machine comprises: - a cylinder block having housings, and - pistons (16) housed in the respective housings, each piston comprising a head (26) and a foot (28), the foot (28) having a largest dimension (Dp) in a direction perpendicular to an axis (PP) of the piston, the largest dimension (Dp) being less than a largest dimension (Dt) of the head in the direction perpendicular to the axis, the foot having a cavity (32) opening onto two opposite sides of the foot at two respective ends of the cavity opposite each other along a main axis (CC) of the cavity. Abstract figure: Fig. 4

Description

Title of the invention: Rotating hydraulic machine equipped with pistons FIELD OF THE INVENTION

[0001] The invention relates to hydraulic machines, in particular their pistons. STATE OF THE ART

[0002] A rotating hydraulic machine generally comprises a cylinder block having housings in which pistons are received. The latter set a fluid in motion or are set in motion by it depending on whether the machine operates as a pump or as a motor.

[0003] An aim of the invention is to improve the operation of rotating hydraulic machines. Statement of the invention

[0004] To this end, according to the invention, a hydraulic machine is provided comprising:

[0005] - a cylinder block having housings, and

[0006] - pistons housed in the respective housings,

[0007] each piston comprising a head and a foot,

[0008] the foot having a larger dimension in a direction perpendicular to an axis of the piston, the larger dimension being less than a larger dimension of the head in the direction perpendicular to the axis,

[0009] the foot having a cavity opening onto two opposite sides of the foot at two respective ends of the cavity opposite one another along a main axis of the cavity.

[0010] The cavity can have several functions depending on the embodiments chosen. It can thus have a function of facilitating the flow of the fluid, a function of softening the piston or both at the same time, as we will see.

[0011] Thus, it can be provided that the cavity allows passage of fluid from one side to the other of the piston foot through the latter.

[0012] This reduces the disturbance of the flow of fluid supplying the housing when leaving the supply duct. This makes it possible to reduce pressure losses. Reducing pressure losses therefore makes it possible to reduce the temperature of the fluid (for the same effort and at equivalent speed). This reduction in temperature makes it possible to limit the rotation speed of the machine less. This also makes it possible to reduce the shear of the fluid, which prevents its premature aging. Thus, the cavity makes it easier to fill the housing with the fluid coming from the supply duct without harming the compactness of the assembly.

[0013] It can be provided that the cavity extends to a free end of the foot.

[0014] It can then be expected that the cavity allows the piston foot to deform more easily.

[0015] It can also be provided that it also makes it possible to increase the passage section between the piston base and the lower bore of the cylinder block.

[0016] On the contrary, it is possible to provide that the cavity extends entirely at a distance from a free end of the foot.

[0017] It can be provided that the cavity is open in the direction opposite to the head.

[0018] It can be provided that the cavity is closed in the direction opposite to the head.

[0019] It can be provided that the cavity is delimited by at least one face oriented in direction opposite to the head.

[0020] It can be provided that the cavity is delimited by at least one cylindrical face having generatrices perpendicular to the axis of the piston.

[0021] It should be remembered in passing that the section of the cavity can be circular, but also rectangular, triangular, etc.

[0022] On the contrary, it is possible to provide that the face is not cylindrical, for example by having an ellipsoidal or oblong longitudinal section.

[0023] It can be provided that the cavity has a circular section.

[0024] It can be provided that the main axis of the cavity is parallel to an axis of rotation of the machine.

[0025] It can be provided that the foot has a circular lateral face cut into by two secondary faces located on either side of the piston axis.

[0026] These faces facilitate the filling of the housing with the fluid in the direction of the piston axis which is radial to the axis of rotation of the machine.

[0027] It can be provided that the secondary faces form cavities.

[0028] Filling with fluid is thus even easier.

[0029] It can be provided that a free end of the foot has a flat face perpendicular to the axis of the piston.

[0030] It can be provided that the machine is configured so that, in a piston position closest to a bottom of the housing, the piston leaves free at least 50% of a section of a mouth of a supply conduit opening into the housing.

[0031] By "leave free" is meant that a projection of the piston on a plane orthogonal to the axis of rotation of the machine does not cover the projection of the mouth of the feed duct on this same plane.

[0032] It can be provided that the machine is configured so that, in the position of each piston closest to the bottom, the piston leaves 100% of the section of the supply duct free.

[0033] Thus the piston foot does not form any obstacle to the entry of fluid into the housing.

[0034] It is possible to provide that the machine is configured so that, in a position of the piston closest to a bottom of the housing, the foot leaves free a passage from one side to another of the foot having over an entire length of the passage a section greater than or equal to 50% of a section of a mouth of a supply conduit opening into the housing.

[0035] It can be provided that the machine is configured so that, in the position of the piston closest to the bottom, the section of the passage is over the entire length of the passage greater than or equal to the section of the mouth.

[0036] It can be provided that the machine is configured so that, in a position of the piston closest to a bottom of the housing, a fluid does not undergo a reduction in passage section when passing from one side of the foot to another.

[0037] It can be provided that the cylinder block has supply ducts extending in a direction parallel to an axis of rotation of the machine.

[0038] This orientation makes it possible to achieve a gain in compactness in the cylinder block compared to a radial orientation of the duct.

[0039] It can be provided that the cylinder block has supply ducts extending in a direction radial to an axis of rotation of the machine.

[0040] It can be provided that the direction is coaxial with the housing.

[0041] It can be provided that the machine comprises for each piston a locking member in rotation of the piston relative to the housing.

[0042] It may be provided that the locking member comprises a guide pin or a clip.

[0043] It may be provided that the locking member extends at the level of the piston foot on one side of the piston opposite a supply duct.

[0044] It can be provided that each housing comprises a head zone and a foot zone, the foot zone being delimited by a main face and having a housing cavity:

[0045] - starting the main face,

[0046] - extending in a direction from a bottom of the housing to the head area, and

[0047] - not ensuring rotational locking of the piston.

[0048] Thus, the housing cavity makes it possible to enlarge the fluid passage section in areas where it should have had a very reduced passage section. It reduces the disturbance of the fluid flow there. The housing cavity thus facilitates the filling of the housing with the fluid, as well as its evacuation. The arrival of the fluid in the housing takes place without prior crushing and makes it possible to initiate the upward movement of the piston. This arrangement makes it possible to reduce the pressure losses and the temperature of the fluid, to limit the rotation speed and to reduce the shear of the fluid.

[0049] It can be predicted that:

[0050] - the housing cavity extends on the same side of the piston as a conduit power supply;

[0051] - the housing cavity has insufficient dimensions to accommodate the pin;

[0052] - the housing does not have a plane of symmetry; and / or

[0053] - the housing cavity opens into the head area.

[0054] It may be provided that the housing cavity extends entirely at a distance from an axis of the housing less than a greater distance separating the head zone and the axis.

[0055] The housing cavity does not necessarily extend in the extension of a face of the head zone of the housing.

[0056] It can be provided that the housing cavity extends entirely at a distance from a median plane of the housing perpendicular to an axis of rotation of the machine.

[0057] Thus, the housing cavity extends outside the functional zone which includes zones of the piston and the housing which are in mutual support in the circumferential direction to the axis of rotation. The position of the housing cavity therefore preserves this zone.

[0058] It can be provided that the housing cavity is cylindrical.

[0059] It can be provided that the housing cavity has an axis parallel to an axis of the accommodation.

[0060] It can be provided that the housing cavity has an axis perpendicular to an axis of the housing.

[0061] It can be provided that the housing cavity has an axis inclined relative to an axis of the housing.

[0062] It may be provided that a supply conduit opens into the housing cavity.

[0063] This arrangement further facilitates the entry of the fluid into the housing as well as its exit. In addition, it reduces the length of the supply conduit. Its machining time is therefore also shortened where appropriate, in compensation for the additional time required for machining the housing cavity.

[0064] It may be provided that a supply conduit of the housing extends at the height of the foot zone with reference to an axis of the housing.

[0065] This is therefore an arrangement in which the conduit does not open into a volume located under the foot zone but directly at the height of the latter.

[0066] It may be provided that the piston comprises a foot having a main face and a secondary face entering the main face of the foot of the piston, the housing cavity having a dimension in a direction perpendicular to an axis of the housing less than a dimension of the secondary face in the direction perpendicular to the axis.

[0067] According to the invention, a piston for a hydraulic machine is also provided,

[0068] the piston comprising a head and a foot,

[0069] the foot having a larger dimension in a direction perpendicular to an axis of the piston, the larger dimension being less than a larger dimension of the head in the direction perpendicular to the axis,

[0070] the foot having a cavity opening onto two opposite sides of the foot at two respective ends of the cavity opposite one another along a main axis of the cavity. DESCRIPTION OF FIGURES

[0071] We will now present embodiments of the invention and variants by way of non-limiting examples in support of the drawings in which:

[0072] - [Fig.l] is an axial sectional view of a machine according to a first mode of realization lization of the invention;

[0073] [Fig.2]

[0074] [Fig.3]

[0075] [Fig.4]

[0076] [Fig.5]

[0077] - Figures 2 to 5 are views of one of the pistons of the machine of [Fig.l];

[0078] [Fig.6]

[0079] [Fig.7]

[0080] - Figures 6 and 7 are cross-sectional and axial views of the piston in its cylinder block housing;

[0081] - [Fig.8] is a view similar to the previous one but schematic showing the passage sections and fluid flows in four parallel planes A, B, C and D;

[0082] [Fig.9]

[0083] [Fig. 10]

[0084] - Figures 9 and 10 are partial sectional views of the cylinder block of the machine and [Fig.l 1] a perspective view of the cylinder block;

[0085] [Fig. 12]

[0086] [Fig. 13]

[0087] - Figures 12 and 13 are diagrams of the functional areas of the cylinder block and of the piston;

[0088] - [Fig. 14] is a view illustrating the stresses in the piston foot;

[0089] [Fig. 15]

[0090] [Fig. 16]

[0091] [Fig. 17]

[0092] [Fig. 18]

[0093] [Fig. 19]

[0094] [Fig.20]

[0095] - figures 15 to 20 are views illustrating alternative embodiments;

[0096] [Fig.21]

[0097] [Fig.22]

[0098] - Figures 21 and 22 are views of another variant showing two positions of the piston in its housing;

[0099] - [Fig.23] is a cross-sectional view of the piston and housing,

[0100] - [Fig.24] shows the passage of the fluid in the housing, and

[0101] - [Fig.25] is a local sectional view of a piston and cylinder block in a second embodiment, showing the stresses of the cylinder block on the piston. Presentation of a first embodiment

[0102] Figures 1 to 14 illustrate a rotating hydraulic machine 2 according to one embodiment of the invention.

[0103] The machine 2 comprises a fixed part and a rotating part mounted to rotate relative to the fixed part around an axis of rotation XX. It thus comprises a casing 4 and a central shaft 6 mounted to rotate relative to the casing by means of bearings 8. A cam 10 is rigidly fixed to the casing. A cylinder block 12 is connected in rotation to the shaft 6. It has housings 14 receiving respective pistons 16 mounted to slide in the housings each in a direction radial to the axis XX. Each piston carries a roller 18 capable of rolling on a track of the cam 10 having for this purpose lobes known per se and not illustrated.

[0104] The machine comprises a distributor 20 connected to a high-pressure fluid circuit and to a low-pressure fluid circuit. For each housing 14, the cylinder block 12 comprises a fluid supply and discharge conduit 22 opening into the housing. The machine is arranged so that the distributor 20 places the supply conduit 22 sometimes in communication with the high-pressure circuit, sometimes with the low-pressure circuit depending on the angular position of the shaft 6 (and therefore of the cylinder block) relative to the casing 4.

[0105] When the housings 14 are supplied in turn with high-pressure fluid, the pressure is communicated to the pistons 16 concerned which slide in their housing and by rolling of the roller 18 against the cam 10 cause the rotation of the rotating part. The machine then operates as a motor to rotate a load. When, on the contrary, the shaft 6 is rotated relative to the casing 4, the shape of the cam 10 causes the pistons 16 to slide in turn, which causes the fluid from each housing 14 to be discharged into the high-pressure circuit. The machine then operates as a pump.

[0106] The invention is applicable to machines having configurations other than this one.

[0107] As illustrated in Figures 2 to 5, each piston 16 comprises a head 26 and a foot or tail 28. It has a main axis PP extending from the head to the foot and which is here oriented in the radial direction to the axis XX. The piston 16 in this case has a general shape with symmetry of revolution around this axis, but this is not obligatory.

[0108] In this example, the foot 28 and the head 26 each have a generally cylindrical shape with a circular section in a plane perpendicular to the axis PP.

[0109] As illustrated in particular in [Fig.4], the foot 28 has a larger dimension Dp in a direction perpendicular to the axis PP. Similarly, the head 26 has a larger dimension Dt in a direction perpendicular to the axis PP. In this case, these are diameters. The larger diameter Dp of the foot 28 is smaller than the larger diameter Dt of the head 26.

[0110] It is therefore a stepped piston 16, itself housed in a stepped housing 14 of complementary shape as illustrated in Figures 6 and 7. As illustrated in Figures 9 and 10, such shapes provide advantages in terms of compactness compared to pistons having a general cylinder shape. Indeed, thanks to the stepped pistons, it is possible to have the same effective displacement while bringing the axes PP of the pistons closer to each other as shown in [Fig. 9]. The angle a in this figure is thus reduced compared to that which would be obtained with non-stepped pistons, namely in which the piston has over its entire length the diameter of the head 26. This shape also brings the housings 14 closer to the axis of rotation XX of the cylinder block 12: the distance d in [Fig. 10] between the bottom 48 of each housing 14 and the internal face 29 of the cylinder block 12 is reduced.

[0111] The head 26 carries the roller 18 coming into contact with the cam 10. For this purpose, it has, for example, a cradle 30 for receiving the roller 18. The cradle 30 has a cylindrical shape having an axis BB parallel to the axis of rotation XX of the machine and a circular section in a plane perpendicular to the axis BB. The cradle is open in the opposite direction to the foot.

[0112] The foot 28 having a cavity 32 having a main axis CC. The cavity opens onto two opposite sides of the foot at two respective ends 34 of the cavity opposite each other along the main axis CC. In this case, the main axis CC of the cavity 32 is parallel to the axis XX of rotation of the machine. In this case, the cavity is open in the opposite direction to the head 26. It extends to a free end of the foot 28 which is opposite the head and is delimited by a cylindrical face 36 oriented in the opposite direction to the head 26. The face 36 has generatrices parallel to the axis CC and perpendicular to the axis PP of the piston 16. The face 36 has a circular section in the species.

[0113] In this case, the foot 28 has a lateral face 40 divided into two cylindrical portions of different diameters along the axis PP since the portion of the foot closest to the head has a reduction in diameter. This face 40 is cut into by two secondary faces 42 located on either side of the axis PP. The secondary faces 42 form cavities in this example. Each of them has a cylindrical shape with generatrices parallel to the axis PP. They each extend from the free end of the foot 28 to the head 26.

[0114] In this case, the free end of the foot 28 has a flat face 44 perpendicular to the axis PP and divided into two portions on either side of the cavity 32.

[0115] The piston 16 here has two planes of symmetry passing through its axis PP and perpendicular to each other.

[0116] With reference to Figures 6 and 7, in the cylinder block 12, the supply ducts 22 have an end 46 forming a mouth opening into the respective housings 14. In this case, each duct 22 has a rectilinear cylindrical shape and extends in a direction parallel to the axis of rotation XX.

[0117] The machine 2 is configured so that, in the position of the piston 16 closest to the bottom 48 of the housing 14, the piston leaves free at least 50% of a section of the mouth 46. As can be seen in [Fig. 8], in this position of the piston 16, the foot 28 provides a passage from one side to another of the foot having over an entire length of the passage a section greater than or equal to 50% of a section of the supply conduit 22 opening into the housing 14. In this case, this section of the passage is greater than or equal to the section of the conduit 22. As the cavity 32 has a cylindrical shape, the fluid does not undergo a reduction in passage section when passing from one side to another of the foot 28 in this position of the piston 16. In particular, [Fig. 8] is a schematic representation of the invention (compared to [Fig.7]) which illustrates the fact that, if we look at the fluid passage section in the lowest position of the piston 16 in the cylinder and particularly the lower portion (i.e. under the plane P orthogonal to the axis of the piston passing through the center of the supply duct), we observe that, thanks to the invention, the fluid passage section through the different planes B, C or D may not be less than the fluid passage section through the plane A. Consequently, the cross-section crossed by the part of the fluid intended to fill the bottom of the housing does not see in its stroke a reduction in section which could lead to pressure losses. On the contrary, for each section plane, the corresponding passage section is never less than the relevant passage section of the duct 22. The flow is therefore improved and flows more easily along an axis parallel to the axis of rotation XX.

[0118] The cavity 32 is arranged so as not to impact the functional surfaces of the piston foot 28. It is known in fact that the piston 16 in its stroke in the housing is subjected to circumferential forces 50, with reference to the axis of rotation XX, due to the rolling of the roller 18 on the cam 10, as illustrated in [Fig.l 1]. On the other hand, it does not undergo axial force 52 along the axis XX. As a result, the housing-piston assembly has a functional zone 54 which undergoes significant forces and for which the contact surface and the quantity of material in contact between the cylinder block 12 and the piston 16 must be preserved. This is an area extending in the circumferential direction on the housing and on the piston as illustrated in figures 12 and 13. This functional zone 54 shown in the drawing for the top of the housing is also true for the piston foot 28.For this reason, the foot 28 allows in its zones oriented along the circumferential direction of the cylinder block a longer guidance of the piston along the axis PP to counter the circumferential forces. On the other hand, the other zones of the foot 28, oriented along the axial direction XX and undergoing less forces, can withstand a release of material. The main cavity 32 and the lateral cavities formed by the secondary faces 42 are located outside this functional zone 54 and therefore do not compromise the performances in this respect.

[0119] The cavity 32 also allows the piston foot 28 to deform more easily. Indeed, in addition to the pressure losses, the releases of material in the non-functional areas of the piston foot provide flexibility to the material. This reduces the stress concentration on the lower part of the foot 28, as shown in [Fig. 14] which illustrates stress concentration levels in the foot 28 during operation. We thus distinguish a favorable deformation zone 56 in the middle part of the face 36 closest to the head 26 of the piston, and a stress concentration zone 58 at the ends of this face.

[0120] The cavity 32 is produced for example by milling. A centering point (not shown) can be produced to allow machining rectification of the piston if necessary. This point has the shape of a blind cavity penetrating into the foot from the face 36 and following the axis PP of the piston. It provides a grip for housing a tip making it possible to immobilize the piston between this tip and another grip (for example another tip housed in the cradle or on the head 26 before production of the cradle). Implementation variants

[0121] We will describe variant embodiments in the following. The characteristics in common with the embodiment described above are not described again.

[0122] In the alternative embodiment of Figures 15 and 16, in the cylinder block 12, the supply duct 22 of each housing 14 extends in a direction radial to the axis of rotation XX. It extends in the direction of the axis PP of the piston. This direction is coaxial with the housing. It opens out at the center of the cavity 32. Indeed, although the invention is of particular interest when the fluid intake / discharge is made by a lateral conduit, it can also be of interest when the supply is made from below along a radial axis. As can be seen in the figures, with a supply from below the piston foot, if the recess is made by sweeping a section of particular shape along an axis parallel to the axis of rotation of the engine (the recess not affecting the functional area of ​​the piston, in particular the piston foot), the fluid supplying the housing does not undergo any obstruction in its path to fill the housing. Here too, it can be provided that the section of the recess is such that it allows the fluid to enter the chamber without having to undergo a reduction in the passage section.

[0123] In the alternative embodiment of [Fig. 17], the cylinder defining the face 36 of the cavity 32 has an open “V” shaped section, giving the cavity a “V” or triangular profile shape.

[0124] In the embodiment variant of [Fig. 18], the cylinder has a rectangular open section.

[0125] In the embodiment variant of [Fig. 19], the cavity 32 is closed in the opposite direction to the head 26 and extends entirely at a distance from the free end of the foot 28. The cavity is in this case cylindrical with a circular section.

[0126] In the embodiment variant of [Fig. 20], the machine comprises for each piston 16 a member for locking the piston in rotation relative to the housing 14. This member here comprises a guide pin. The pin, also illustrated in [Fig. 3], extends on one side of the piston opposite the supply duct 22. It is partially mounted in a blind duct formed in one of the secondary faces 42. The duct has an elongated shape, for example in a direction radial to the axis PP of the piston. The pin extends projecting from this face and from the envelope surface of the foot. It is received in a secondary housing 62 of the housing, this housing being elongated in a direction parallel to the axis PP.

[0127] In the variant of figures 21 to 24, the piston 16 is identical to that of figures 2 to 4. This variant differs with regard to the housing 14 of the piston.

[0128] Each housing 14 comprises a head zone 66 and a foot zone 68 respectively accommodating the head 26 and the foot 28 of the piston, having shapes complementary to these parts of the piston. Thus, the foot zone has a diameter in the direction perpendicular to the axis PP of the housing smaller than the diameter of the head zone 66 in the same direction.

[0129] The foot zone 68 is delimited by a main face 70, in this case cylindrical with a circular section in a plane perpendicular to the axis PP.

[0130] It has a secondary cavity 72:

[0131] - entering the main face 70,

[0132] - extending in a direction from a bottom 48 of the housing to the head zone 66, and

[0133] - not ensuring rotational locking of the piston 16.

[0134] The secondary cavity 72 is in this case cylindrical, it has an axis parallel to the axis PP of the housing and its section in a plane perpendicular to this axis is circular in this example. But this section could be rectangular, triangular or have another shape.

[0135] In this case, the secondary cavity 72 opens into the head zone 66 via one of its axial ends.

[0136] It extends entirely at a distance from the axis PP of the housing 14 less than a greater distance separating the head zone 66 and the axis PP. Thus it is not in the extension of a face of the head zone. The cavity 72 extends entirely at a distance from a median plane of the housing perpendicular to the axis of rotation XX. It is here intercepted by a plane radial to this axis. The secondary cavity 72 is therefore arranged so as not to impact the functional surfaces of the foot zone 68.

[0137] With reference to figures 21 and 22, in the cylinder block 12, the supply ducts 22 have an end 46 forming a mouth opening into the respective housings 14. In this case, each duct 22 has a rectilinear shape and extends in a direction parallel to the axis of rotation XX. The supply duct 22 opens into the secondary cavity 72 and extends at the height of the foot zone with reference to the axis PP of the housing.

[0138] Figures 21 and 22 illustrate respectively the low and high positions of the piston 16 in the housing 14. As seen in [Fig. 21], in the low position, which is the position of the piston closest to the bottom 48 of the housing, the foot 28 of the piston extends away from the mouth 46 of the supply duct 22, which it leaves clear, in particular due to the presence of the secondary cavity 72. The latter allows the fluid arriving in the foot zone 68 in motor mode to fill the housing and reach the head 26 of the piston with reduced disturbances and therefore little pressure loss, as illustrated in [Fig. 24]. Thus, the fluid passage section is larger near the supply duct 22. This also reduces pressure loss at the discharge. Indeed, the same advantage exists in pump mode when the piston propels the fluid out of the housing into the conduit 22, which then serves for discharge.

[0139] As illustrated in [Fig.23], each lateral cavity formed by the lateral face 42 of the piston has a dimension lc, in a direction perpendicular to the axis PP of the housing, less than the dimension lp, in the same direction, of the secondary cavity 72 of the housing located opposite. This arrangement makes it possible to avoid, during the machining of the secondary cavity 72, generating a burr in a functional sliding zone of the piston foot 28. This also allows simpler milling, if necessary.

[0140] As in the variant of [Fig.20], the piston comprises a pin 60 received in a groove 62 of the housing in order to prevent rotation of the piston in the housing. Unlike the groove 62, the secondary cavity 72 has dimensions, in particular a depth in a plane perpendicular to the axis PP, insufficient to accommodate the pin 60, which provides a foolproofing when receiving the piston in its housing. Indeed, the operator cannot place the piston in its housing by attempting to insert the pin in the secondary cavity. The groove 62 and the cavity 72 are located on either side of the median plane of the cylinder block 12 but are not diametrically opposed on either side of the axis PP. Thus, the root zone 68 does not have a plane of symmetry. Their position around the axis here forms an angle of approximately 150°.

[0141] The cylinder block 12 can be manufactured by giving it its general shape using conventional methods, in particular by machining and / or casting. In this case, the secondary cavity 72 and the groove 62 are produced in the foot zone by removing material using the same tool, for example the same milling cutter. Second embodiment

[0142] Another embodiment of the machine has been illustrated in [Fig. 25]. Only the characteristics of the machine which differ from those of the first embodiment will be presented. The main difference lies in the production of the cavity 32 opening onto two opposite sides of the foot 28 in the form of a groove. This is therefore a reduction in the dimensions of the section of the cavity in a plane perpendicular to its axis CC, compared with the first embodiment, the length along this axis remaining unchanged. The cavity has, for example, the shape of a parallelepiped having a section in a plane perpendicular to the axis CC which is very thin in a direction perpendicular to the axis XX of the machine. The cavity extends from the free end of the piston foot. It is delimited by two plane faces parallel to each other and parallel to a direction radial to the axis XX.It looks like a cavity that would be obtained by means of a saw cut given in the piston from the piston foot. It can be obtained by this means or by others.

[0143] During operation of the hydraulic machine (during the relative rotation of the cylinder block 12 and the cam 10), the pistons 16 are subjected to tilting forces F relative to their translation axis PP. The tilting forces F are applied in planes perpendicular to the axis XX of the relative rotation of the cylinder block and the cam. The cradle-shaped recesses 30 at the top of the pistons are oriented parallel to this axis to allow the rollers 18 present in these recesses to roll against the cam. The cavity 32 made in the piston base 28 is also parallel to the axis XX of the relative rotation of the cylinder block and the cam. Due to the presence of this additional cavity in the piston base, the parts of the guide surface that border this cavity in the piston foot have a slight flexibility that allows them to deform in planes perpendicular to the axis (CC) of the cavity. It is therefore precisely in the planes in which the tilting forces F are significant that these parts of the guide surface can be slightly deformed and the contact surfaces increased. This makes it possible to limit the negative impact of the tilting forces by increasing the contact surface, thus reducing the contact pressures and avoiding excessive localized friction. This makes it possible to reduce the wear of the hydraulic machine at the level of the pistons and the cylinder block. This flexibility can be obtained by giving other shapes to the cavity.

[0144] Numerous modifications may be made to the invention without departing from its scope.

Claims

Claims

1. Hydraulic machine (2) comprising: - a cylinder block (12) having housings (14) and fluid supply conduits for the respective housings, and - pistons (16) housed in the respective housings, each piston comprising a head (26) and a foot (28), the foot (28) having a largest dimension (Dp) in a direction perpendicular to an axis (PP) of the piston, the largest dimension (Dp) being less than a largest dimension (Dt) of the head in the direction perpendicular to the axis, the foot having a cavity (32) in communication with the supply conduit of the piston housing, the cavity opening onto two opposite sides of the foot at two respective ends (46) of the cavity opposite each other along a main axis (CC) of the cavity.

2. Machine according to the preceding claim in which the cavity (32) extends to a free end of the foot (28).

3. Machine according to claim 1 in which the cavity (32) extends entirely at a distance from a free end of the foot (28).

4. Machine according to at least one of the preceding claims in which the cavity (32) is delimited by at least one face (36) oriented in the direction opposite to the head (26).

5. Machine according to at least one of the preceding claims in which the cavity (32) is delimited by at least one cylindrical face (36) having generatrices perpendicular to the axis (PP) of the piston.

6. Machine according to at least one of the preceding claims in which the cavity (32) has a circular section.

7. Machine according to at least one of the preceding claims in which the main axis (CC) of the cavity (32) is parallel to an axis of rotation (XX) of the machine.

8. Machine according to at least one of the preceding claims in which the foot (28) has a circular lateral face (40) cut into by two secondary faces (42) located on either side of the axis (PP) of the piston.

9. Machine according to the preceding claim in which the secondary faces (42) form cavities.

10. Machine according to at least one of the preceding claims in which the machine is configured so that, in a piston position (16) closest to a bottom (48) of the housing, the piston leaves free at least 50% of a section of a mouth (46) of a supply conduit opening into the housing.

11. Machine according to the preceding claim in which the machine is configured so that, in the position of each piston (16) closest to the bottom, the piston leaves 100% of the section free.

12. Machine according to at least one of the preceding claims in which the machine is configured so that, in a position of the piston (16) closest to a bottom (48) of the housing, the foot (28) leaves free a passage from one side to another of the foot having over an entire length of the passage a section greater than or equal to 50% of a section of a mouth (46) of a supply conduit opening into the housing.

13. Machine according to at least one of the preceding claims in which the machine is configured so that, in a position of the piston (16) closest to a bottom (48) of the housing, a fluid does not undergo a reduction in passage section when passing from one side to another of the foot (28).

14. Machine according to at least one of the preceding claims in which the cylinder block (12) has supply ducts (22) extending in a direction parallel to an axis of rotation (XX) of the machine.

15. Machine according to at least one of claims 1 to 14 in which the cylinder block (12) has supply ducts (22) extending in a direction radial to an axis of rotation (XX) of the machine.

16. Machine according to at least one of the preceding claims which comprises for each piston (16) a member (60) for locking the piston (16) in rotation relative to the housing (14).

17. Machine according to the preceding claim in which the locking member extends at the level of the piston foot on one side of the piston (16) opposite a supply duct (22).

18. Machine according to the preceding claim in which the locking member (60) comprises a guide pin.

19. Machine according to at least one of the preceding claims in which each housing comprises a head zone (66) and a foot zone (68), the foot zone being delimited by a main face (70) and having

20.

21.

22.

23. a housing cavity (72): - starting the main face (70), - extending in a direction from a bottom (48) of the housing to the head zone, and - not ensuring a rotational lock of the piston. Machine according to the preceding claim in which the housing cavity (72) extends on the same side of the piston as a supply duct (22). Machine according to claim 18 and one of claims 19 and 20 in which the housing cavity (72) has dimensions insufficient to accommodate the pin. Machine according to at least one of the preceding claims, in which the housing (14) does not have a plane of symmetry. Piston (16) for hydraulic machine, the piston comprising a head (26) and a foot (28), the foot having a greater dimension (Dp) in a direction perpendicular to an axis (PP) of the piston, the greater dimension being less than a greater dimension (Dt) of the head in the direction perpendicular to the axis, the foot having a cavity (32) opening into a zone of the piston arranged to be subjected to a pressure of a hydraulic fluid, the cavity opening onto two opposite sides of the foot at two respective ends (46) of the cavity opposite one another along a main axis (CC) of the cavity.

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