Improved Sealing Device for Hydraulic Machinery

Abstract

A hydraulic machine (1) comprising a first assembly (10) and a second assembly (20) rotatable relative to each other along a rotation axis (XX), the hydraulic machine (1) comprising a crankcase defining an internal volume (2), the interface between the fixed assembly and the movable assembly having a housing (4) comprising a first dynamic sealing element (40) ensuring sealing of the internal volume (2) against the external environment, the hydraulic machine (1) characterized in that a second dynamic sealing element (6) is arranged between the internal volume (2) and the housing (2), the second sealing element (6) being adapted to allow passage of a fluid from the internal volume (2) to the housing (4) when a pressure deviation between the internal volume (2) and the housing (4) is less than or equal to a pressure threshold, and to isolate the housing (4) from the internal volume (2) when the pressure deviation is greater than the pressure threshold.

Description

Technical Field

[0001] The present disclosure relates to an improved sealing device for a hydraulic machine, and more specifically, to a sealing protection device against peak pressure.

Background Art

[0002] Since rotating machines are used in various environments, ensuring airtightness has been a problem. In fact, preventing impurities from being taken into the internal volume of the crankcase of a rotating machine has repeatedly been an issue.

[0003] To ensure good airtightness between the internal volume of a rotating machine and the external environment, various sealing structures have been proposed. However, known solutions still have problems in terms of reliability, especially reliability over time.

[0004] The first attachment consists of arranging a single sealing element that isolates the peripheral environment from the internal volume of the crankcase. However, when the pressure inside the crankcase rises, the sealing element may be pushed out of the housing, or in the case of a metal seal, the bearing force between the two sliding parts increases, so the sliding contact surfaces may crack or seize, and there is a possibility of being destroyed. As a result, in the case of a metal seal, the friction increases and the efficiency deteriorates. Such an increase in pressure inside the crankcase occurs, for example, when starting a low-temperature hydraulic machine. The pressurized oil enters the crankcase of the machine from frequent internal leakage in these machines, and the oil in the crankcase cannot easily flow out from the crankcase drain pipe, which is still filled with low-temperature oil. Due to the high viscosity of this low-temperature oil, a very high pressure drop occurs. By such an operation, the sealing element is rapidly destroyed. In particular, when the pressure inside the crankcase of the machine rises, the bearing force between the sliding parts of the sealing element increases, and in the case of a flexible sealing element, seizure or extrusion may occur, and the sealing element may be destroyed. Also, the components of the sealing element may be destroyed by this pressure.

[0005] Alternatively, the pollution prevention sealing element that isolates between the surrounding environment and the internal volume of the crankcase can be arranged in a dedicated housing, and these housings themselves are generally called absolute sealing, which combines a dynamic sealing element such as a lip ring and a dynamic sealing element that can withstand the peak pressure that may occur (such as an O-ring coupled to an annular element), and is isolated from the internal volume of the crankcase including a rotating machine (such as a hydraulic machine) by the crankcase sealing. By such an attachment, a closed chamber is formed between the axial sealing element and the crankcase sealing element. However, such a closed chamber poses a problem in terms of lubrication. In fact, since the housing with the axial sealing element is completely isolated from the internal volume of the crankcase by the crankcase sealing, this housing is not continuously lubricated, especially when lubrication is lost over time or its characteristics deteriorate. Lack of lubrication can lead to rapid destruction of the sealing element, especially under the influence of seizure or extrusion due to lack of oil. A commonly proposed solution is to insert a predetermined amount of oil into this housing, and this oil needs to be replaced regularly. Also, since this housing needs to have a sufficient volume, the compactness of the hydraulic machine is impaired. Such a solution is very restrictive and it is understood that dedicated maintenance work is required. Summary of the Invention Problems to be Solved by the Invention

[0006] Therefore, the present disclosure aims to at least partially address these problems. Means for Solving the Problems

[0007] For this reason, the present disclosure is a hydraulic machine including a first assembly and a second assembly that are rotatable relative to each other along a rotation axis, the hydraulic machine including a crankcase that defines an internal volume, In a hydraulic machine having a housing in which an interface between a fixed assembly and a movable assembly includes a first sealing element for ensuring the sealing of an internal volume with respect to an external environment, a second sealing element is disposed between the internal volume and the housing, and the second sealing element is adapted to allow fluid to pass from the internal volume to the housing when a pressure deviation between the internal volume and the housing is below a pressure threshold, and to prevent fluid from passing from the internal volume to the housing when the pressure deviation between the internal volume and the housing exceeds the pressure threshold. The present invention relates to a hydraulic machine.

[0008] According to one example, the second sealing element has a passage that is adapted to close when the pressure in the internal volume or the pressure in the housing exceeds a threshold, or when, for example, a pressure difference between the internal volume and the housing exceeds a threshold, typically 0.1, 0.2 or 0.5 bar.

[0009] According to one example, the first sealing element is an axial seal comprising a first metal annular part, a second metal annular part, a first elastomeric annular part, and a second elastomeric annular part, the first metal annular part and the second metal annular part being supported and attached to each other along an axial direction defined by a rotation axis, the first elastomeric annular part being interposed between the first metal annular part and a wall of the first assembly, and the second elastomeric annular part being interposed between the second metal annular part and a wall of the second assembly.

[0010] According to one example, the second sealing element comprises an O-ring.

[0011] And the second sealing element typically comprises a ring on which the O-ring is placed.

[0012] And the ring typically has a bore that allows fluid passage when the pressure deviation between the internal volume and the housing is below the pressure threshold and prevents fluid passage when the pressure deviation between the internal volume and the housing is greater than the pressure threshold.

[0013] According to one example, the second sealing element is disposed between two rotating elements that ensure relative rotational movement between the first assembly and the second assembly.

[0014] According to one example, the second sealing element is integrally formed.

[0015] According to one example, the second sealing element is adapted to allow fluid passage from the housing to the internal volume when the pressure deviation between the internal volume and the housing is below the pressure threshold and to isolate the housing from the internal volume when the pressure deviation between the internal volume and the housing is greater than the pressure threshold.

[0016] According to one example, the second sealing element is interposed between two surfaces facing each other along an axial direction defined by a rotation axis.

[0017] According to one example, the second sealing element is interposed between two surfaces facing each other along a radial direction with respect to the rotation axis.

[0018] According to one example, the pressure threshold is equal to 0.5 bar, or 0.2 bar, or even 0.1 bar.

[0019] The hydraulic machine is, for example, a machine comprising a cylinder block having a plurality of housings extending radially with respect to a rotation axis in which cylinders are disposed, and a multi-lobe cam surrounding the cylinder block.

[0020] The present invention and its advantages will be better understood by reading the following detailed description of various embodiments of the present invention given as non-limiting examples.

Brief Description of the Drawings

[0021]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

[0022] In all the figures, common elements are denoted by the same reference numerals.

Modes for Carrying Out the Invention

[0023] Hereinafter, an exemplary embodiment of the present invention will be described with reference to FIGS. 1 to 5.

[0024] Figure 1 shows a cross-sectional view of the hydraulic machine 1, which is typically a radial piston and multi-lobe cam hydraulic machine. A hydraulic machine typically means a hydraulic motor or a hydraulic pump, and these devices typically operate reversibly. The hydraulic machine 1 includes a distributor cover 110, a supply distributor 112, a cylinder block 114, and an assembly generally called a hydraulic torque including a piston 116 having bearing rollers 118, a multi-lobe cam 120, a shaft 122, a bearing 124 consisting of a bearing assembly, and a bearing cover 126. The shaft 122 is mechanically connected to the cylinder block 114 and transmits the rotational movement caused by the torque applied to the shaft 122 or the sliding of the piston 116 in contact with the multi-lobe cam 120. The distributor cover 110 includes supply ducts for the suction and delivery of the hydraulic machine 1. The suction duct and the delivery duct, the ducts of the distributor, and the piston chambers of the cylinder block are connected to a hydraulic circuit that transmits hydraulic power. For example, they are connected to the supply branch and the return branch of a closed-loop hydraulic circuit, or to the high-pressure HP branch and the low-pressure LP branch of a closed-loop hydraulic circuit, or for an open-loop hydraulic circuit, to the supply line by a power pump and the return line to the tank. In the illustrated example, the distributor cover 110, the cam 120, and the bearing cover 126 form the crankcase of the hydraulic machine 1.

[0025] The volume contained in the crankcase around the various elements described above represents the internal volume of the hydraulic machine 1. It is represented by hatching in Figure 1. This is isolated from the hydraulic power circuit (represented by the dotted line) by the sealing of the piston 116 and the distributor 112 in a manner well known to those skilled in the art. The internal volume of the hydraulic machine 1 receives the oil flow rate resulting from the internal leakage of the hydraulic machine 1 coming from the power circuit and typically discharges this oil flow rate to a tank so that the pressure of the internal volume of the hydraulic machine 1 remains substantially equal to the pressure of the tank, which is typically equal to or close to atmospheric pressure, by means of a drain.

[0026] Figure 2 shows a partial cross-sectional view of the hydraulic machine 1. The hydraulic machine 1 includes a first assembly 10 and a second assembly 20 that are rotatable relative to each other along the rotation axis X-X. In the following description, the terms "radial direction" and "axial direction" are defined based on the rotation axis X-X unless otherwise specified.

[0027] In the illustrated example, the rotational movement is ensured by a rotating element, here the tapered bearings 32 and 34 that form the bearing 30. The hydraulic machine 1 has an internal volume 2 in which different components 3 of the hydraulic machine (such as a radial piston hydraulic motor or an axial piston hydraulic motor, a radial piston hydraulic pump or an axial piston hydraulic pump, a braking system, or other devices) are arranged according to its nature.

[0028] The first assembly 10 and the second assembly 20 represent different components of the hydraulic machine. As an example, one of these assemblies may include the shaft, cylinder block, and distributor of the hydraulic machine, and the other of these assemblies may include a multi-lobe cam. The first assembly 10 and the second assembly 20 may include braking means, for example, a disk adapted to prevent the relative rotational movement of the first assembly 10 with respect to the second assembly 20 under the influence of friction between the disks.

[0029] The internal volume 2 of the hydraulic machine is isolated from the external environment via a first sealing element 40 arranged in the housing 4. The housing 4 is connected to the external environment via a duct 5 formed by a gap between the first assembly 10 and the second assembly 20. In the illustrated example, the first sealing element 40 is an axial seal, generally called a duo-cone seal, or a floating seal.

[0030] The first sealing element 40 includes a first metal annular portion 41 and a second metal annular portion 43 made of a metal material, and these metal annular portions are typically symmetric with respect to a plane extending in the radial direction with respect to the rotation axis X-X. The first sealing element 40 also includes a first elastomeric annular portion 42 and a second elastomeric annular portion 44 made of an elastomeric material.

[0031] The first metal annular portion 41 and the second metal annular portion 43 support each other along the axial direction defined by the rotation axis X-X.

[0032] The first elastomeric annular portion 42 is supported and attached to the first metal annular portion 41 on one hand and to the partition 14 of the first assembly 10 on the other hand.

[0033] The second elastomeric annular portion 44 is supported and attached to the second metal annular portion 43 on one hand and to the partition 24 of the second assembly 20 on the other hand.

[0034] The first elastomeric annular portion 42 and the second elastomeric annular portion 44 are typically arranged radially outside the first metal annular portion 41 and the second metal annular portion 43. The first metal annular portion 41 and the second metal annular portion 43 press the first elastomeric annular portion 42 and the second elastomeric annular portion 44 against the respective partitions 14 and 24 of the first assembly 10 and the second assembly 20, thus ensuring a sealed connection.

[0035] The first metal annular portion 41, the second metal annular portion 43, and the respective partitions 14 and 24 of the first assembly 10 and the second assembly 20 are typically formed such that the first elastomeric annular portion 42 and the second elastomeric annular portion 44 can easily move the first metal annular portion 41 and the second metal annular portion 43 relative to each other along the axial direction defined by the rotation axis X-X.

[0036] As shown above, the problem with this type of attachment relates to the lubrication of the first sealing element 40. In fact, in the conventional structure, the housing 4 is typically isolated from the internal volume of the crankcase 1 by a seal recognized as an absolute seal, which generally includes a reinforced seal adapted to withstand in particular any peak pressure, for example a dynamic seal combined with a lip ring. However, with such an attachment, since the housing 4 is completely isolated from the internal volume of the crankcase 1, it is necessary to provide lubrication from the design stage, for example by inserting a predetermined amount of oil into the housing 4. However, in this case, as long as the oil gradually leaks out to the external environment, regular maintenance work is required to reintroduce the oil into the housing 4. Furthermore, with such a structure, there is a problem that when a peak pressure occurs in the internal volume of the crankcase 1, the sealing element disposed in the housing 4 may be damaged.

[0037] In the structure proposed by the present disclosure, it is proposed to dispose a second sealing element 6 between the internal volume 2 and the housing 4, rather than an absolute seal. The proposed second sealing element 6 allows the passage of fluid from the internal volume 2 to the housing 4 when the pressure in the internal volume 2 is below a pressure threshold, and isolates the housing 4 from the internal volume 2 when the pressure deviation between the internal volume 2 and the housing 4 is greater than the pressure threshold, and thus is adapted not to allow fluid to pass from the internal volume 2 to the housing 4 when the pressure deviation between the internal volume 2 and the housing 4 is greater than the pressure threshold. Thus, the second sealing element 6 has the function of a calibrated valve or a two-way stream nozzle.

[0038] The passage of the second sealing element is also capable of acting in the reverse direction, so that when the pressure in the internal volume rises, especially when heating occurs, oil can pass from the housing into the internal volume. Such operation in both flow paths does not adversely affect the lubrication of the housing 4.

[0039] Therefore, when the pressure deviation between the internal volume 2 and the housing 4 is below a predetermined pressure threshold, the second sealing element 6 can achieve a calibrated flow of oil from the internal volume 2 to the housing 4. Thus, the second sealing element 6 typically has a passage and allows fluid circulation between the internal volume 2 and the housing 4 as long as the pressure is below the pressure threshold, and closes when the pressure deviation between the housing 4 and the internal volume 2 exceeds the pressure threshold, isolating the internal volume 2 from the housing 4. More generally, the second sealing element 6 is adjusted so that the fluid flow rate through the housing 4 does not lead to an excessive pressure increase in the housing 4. According to one example, when the pressure values in the housing 4 and the internal volume 2 before the peak pressure in the internal volume 2 are 3 bar, the second sealing element can be adjusted to raise the pressure in the housing 4 by approximately 0.2 bar and allow passage from a pressure of 3 bar to a pressure of 3.2 bar.

[0040] This function can ensure continuous lubrication of the housing 4 while protecting the first sealing element 40 against the peak pressure in the internal volume 2. In fact, when the pressure in the internal volume 2 reaches its peak, the second sealing element 6 does not allow fluid to pass through and operates like an absolute seal, preventing a pressure that is too high and could cause deterioration of the first sealing element 40 from reaching the housing 4.

[0041] The pressure threshold value is, for example, 2.5 to 3.5 bar, more specifically 3 to 3.2 bar. More generally, the operation in the mode of allowing the fluid to pass through or not to pass through may depend on the pressure difference across the second sealing element 6, for example, when the pressure difference is 0.5 bar or more, or 0.2 bar or more, or even 0.1 bar or more.

[0042] Conversely, when the pressure inside the internal volume 2 does not exceed the pressure threshold value, the second sealing element 6 allows the fluid to pass through. When heating occurs within the housing 4, the increase in this pressure is moderated, and the oil flows towards the internal volume 2 before the peak pressure occurs. In this way, the pressure within the housing 4 does not exceed the pressure of the internal volume 2 as long as the pressure of the internal volume 2 is lower than the pressure threshold value. There is no possibility of the pressure within the housing 4 itself increasing. Also, the risk of the first sealing element 40 being damaged or the oil jetting out due to the increase in pressure within the housing 4 is eliminated.

[0043] The second sealing element 6 can be arranged, for example, between two rotating elements forming the rolling bearing 30 of the hydraulic machine 1, between the rolling bearing 30 and the housing 4, or between the internal volume 2 and the rolling bearing 30.

[0044] Next, an exemplary embodiment of the second sealing element 6 will be described with reference to FIGS. 3, 4, and 5. The two functions of the second sealing element 6, namely the sealing function and the fluid passage function, are here performed by the same component.

[0045] These figures here show the second sealing element 6, which is composed of a ring 61 and an O-ring 63. The second sealing element 6 is arranged in a groove 7 formed at the interface between the first assembly 10 and the second assembly 20. The groove 7 can extend radially or axially with respect to the rotation axis X-X. The examples shown in FIGS. 3, 4, and 5 represent grooves that extend radially with respect to the rotation axis X-X. However, it is understood that the operation for an axial groove is the same. A structure having an axial groove is shown below. The groove 7 is interposed between the internal volume 2 and the housing 4.

[0046] The ring 61 typically forms an annular portion around the rotation axis X-X. It can have a rectangular cross-section (as seen in FIG. 3), or a rectangular cross-section with a protrusion 64 adapted to contact the wall of the first assembly 10 or the second assembly 20 (as seen in FIG. 5). One or several bores 62 are formed in the ring 61, and these bores 62 are adapted to allow fluid to pass through the ring 61, thus forming the above-mentioned passage for the second sealing element 6.

[0047] The ring 61 has a thickness that is strictly greater than the distance between the first assembly 10 and the second assembly 20 around the groove 7, either along the axial direction or along the radial direction, depending on the orientation of the groove 7.

[0048] In the illustrated example, the first assembly 10 and the second assembly 20 are spaced apart by a gap E1 on both sides of the groove 7 in the radial direction with respect to the rotation axis X-X. Therefore, the ring 61 has a radial thickness E2 that is strictly greater than E1 so that the ring 61 does not come out of the groove 7. The groove 7 has a radial dimension that is strictly greater than E2 so that the ring 61 and the O-ring 63 can be accommodated therein.

[0049] The O-ring 63 may have a circular cross-section, an elliptical cross-section, or other cross-sections. In the examples shown in FIGS. 3, 4, and 5, the O-ring 63 has a circular cross-section and is disposed around the ring 61, that is, in contact with the ring 61 and arranged to surround it radially outward with respect to the rotation axis X-X.

[0050] FIG. 4 is a diagram showing the influence when the pressure in the internal volume 2 reaches a peak.

[0051] The arrows schematically show the influence of the peak pressure on different elements of the second sealing element 6. As can be seen from this figure, the O-ring 63 is pressed against the axial wall of the groove 7, here the wall of the groove 7 on the side opposite to the internal volume 2. The pressure increase in the groove 7 also causes the ring 61 to be crushed under the influence of the pressure and under the influence of the O-ring 63 that compresses the ring 61.

[0052] This crushing of the ring 61 causes deformation of the ring 61, whereby the bore 62 is blocked when the pressure is greater than the pressure threshold, thus preventing the passage of fluid through the second sealing element 6.

[0053] Also, this operation is reversible, and it is understood that the same function is executed when the pressure in the housing 4 increases with respect to the internal volume 2. When the pressure in the housing 4 is below the pressure threshold (or when the pressure difference between the housing 4 and the internal volume 2 exceeds the threshold), the second sealing element 6 allows the passage of fluid from the housing 4 to the internal volume 2, and when the pressure in the housing 4 is greater than the pressure threshold, it isolates the internal volume 2 from the housing 4, thereby being adapted to prevent the intrusion of impurities into the internal volume 2.

[0054] FIG. 6 shows a variant of the embodiment already described with reference to FIG. 2. The sealing between the first assembly 10 and the second assembly 20 is ensured by an absolute seal and a second sealing element 6 as defined above.

[0055] In this exemplary embodiment, at the interface between the first assembly 10 and the second assembly 20, an absolute seal 8 is formed between the housing 4 and the internal volume 2. This absolute seal 8 isolates the housing 4 from the internal volume 2, and by this sealing, any passage of fluid between these two volumes is prevented.

[0056] The second sealing element 6 is arranged in a bypass duct 60 formed in the first assembly 10 or the second assembly 20, and thus, as described above, the passage of fluid can be ensured in the form of a calibration valve or a two-way flow nozzle.

[0057] Its operation is the same as the operation already described with reference to FIGS. 2 to 5.

[0058] The bypass duct 60 can be formed, for example, here, by a bore that opens into a valve that forms an outer calibration valve or an outer two-way flow nozzle (for example, a metal valve having two tubes) that constitutes the second sealing element 6.

[0059] FIG. 7 shows a variant of the embodiment already described with reference to FIG. 2.

[0060] In this embodiment, the groove 7 is formed along the axial direction of the rotation axis X-X.

[0061] Therefore, the second sealing element 6 extends along the axial direction rather than the radial direction. Considering the second sealing element 6 provided with the ring 61 and the O-ring 63 as described above, the ring 61 and the O-ring 63 are stacked along the axial direction.

[0062] Its operation is the same as the operation already described with reference to FIGS. 2 to 5.

[0063] The structure thus proposed makes it possible to protect the tightness of the rotary machine by isolating the internal volume from the ambient environment not only from the pressure rise within the internal volume, but also from insufficient lubrication within the housing and from the pressure rise within the housing due to heating. Thus, as long as the lubrication of the first sealing element 40 is ensured by the oil coming from the internal volume of the hydraulic machine, the housing no longer needs to perform the oil storage and reserve functions, so that the housing can be reduced. The hydraulic machine is more reliable, less bulky and does not require specific maintenance of the oil within the housing.

[0064] Although the present invention has been described with reference to specific exemplary embodiments, it will be apparent that modifications and changes can be made to these examples without departing from the general scope of the invention as defined by the claims. In particular, the individual features of the different embodiments shown / mentioned can be combined in additional embodiments. Accordingly, the description and drawings are to be considered in an illustrative rather than a limiting sense.

[0065] It is also clear that all the features described with reference to one method can be transposed, alone or in combination, to one device, and conversely, all the features described with reference to one device can be transposed, alone or in combination, to one method.

Claims

1. A hydraulic machine (1) comprising a first assembly (10) and a second assembly (20) rotatable relative to each other along a rotation axis (X-X), wherein the hydraulic machine (1) comprises a crankcase defining an internal volume (2), and a housing (4) having an interface between a fixed assembly and a movable assembly, the interface comprising a first dynamic sealing element (40) for ensuring the sealing of the internal volume (2) against the external environment. In the hydraulic machine (1), a second dynamic sealing element (6) is arranged at the interface between the fixed assembly and the movable assembly between the internal volume (2) and the housing (4), and the second dynamic sealing element (6) is adapted to allow the passage of oil from the internal volume (2) to the housing (4) to lubricate the first dynamic sealing element (40) by the fluid coming from the internal volume when the pressure deviation between the internal volume (2) and the housing (4) is less than a pressure threshold value, and is adapted not to allow the passage of oil from the internal volume (2) to the housing (4) when the pressure deviation between the internal volume (2) and the housing (4) exceeds the pressure threshold value. Characterized in that, the hydraulic machine (1).

2. The hydraulic machine (1) according to claim 1, wherein the second dynamic sealing element (6) has a passage adapted to be closed when the pressure deviation between the internal volume (2) and the housing (4) exceeds the pressure threshold value.

3. The first dynamic sealing element (40) is an axial seal comprising a first metal annular part (41), a second metal annular part (43), a first elastomeric annular part (42), and a second elastomeric annular part (44), wherein the first metal annular part (41) and the second metal annular part (43) are supported and attached to each other along the axial direction defined by the rotation axis (X-X), the first elastomeric annular part (42) is interposed between the first metal annular part (41) and the wall (14) of the first assembly, and the second elastomeric annular part (44) is interposed between the second metal annular part (43) and the wall (24) of the second assembly (20). The hydraulic machine (1) according to claim 1.

4. The hydraulic machine (1) according to claim 1, wherein the second dynamic sealing element (6) comprises an O-ring (63).

5. The hydraulic machine (1) according to claim 4, wherein the second dynamic sealing element (6) comprises a ring (61) on which the O-ring (63) is placed.

6. The hydraulic machine (1) according to claim 5, wherein the ring (61) has a bore (62) adapted to allow oil to pass when the pressure deviation between the internal volume (2) and the housing (4) is below the pressure threshold and to prevent oil from passing when the pressure deviation between the internal volume (2) and the housing (4) exceeds the pressure threshold.

7. The hydraulic machine (1) according to claim 1, wherein the second dynamic sealing element (6) is arranged between two rotating elements (32, 34) that ensure relative rotational movement between the first assembly (10) and the second assembly (20).

8. The hydraulic machine (1) according to claim 1, wherein the second dynamic sealing element (6) is integrally formed.

9. The hydraulic machine (1) according to claim 1, wherein the second dynamic sealing element (6) allows oil to pass from the housing (4) to the internal volume (2) when the pressure deviation between the internal volume (2) and the housing (4) is below the pressure threshold, and is adapted to isolate the housing (4) from the internal volume (2) when the pressure deviation between the internal volume (2) and the housing (4) is greater than the pressure threshold.

10. The hydraulic machine (1) according to claim 1, wherein the second dynamic sealing element (6) is interposed between two surfaces facing each other along the axial direction defined by the rotation axis (X-X).

11. The hydraulic machine (1) according to claim 1, wherein the second dynamic sealing element (6) is interposed between two surfaces facing each other along the radial direction with respect to the rotation axis (X-X).

12. The hydraulic machine (1) according to claim 1, wherein the pressure threshold is equal to 0.5 bar, or more precisely 0.2 bar.

13. The hydraulic machine (1) according to claim 1, comprising a cylinder block having a plurality of housings extending radially with respect to a rotation axis (X-X) in which cylinders are arranged, and a multi-lobe cam surrounding the cylinder block.

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