Hydraulic machine comprising a stack of discs acted upon by push rods

Abstract

Hydraulic machine comprising: - a fixed part; - a part mounted in rotation relative to the fixed part about an axis (O-O); - a stack (50) of discs (53, 54) forming a brake or a clutch, the discs being able to abut against each other by means of friction surfaces (88) having an average friction radius (Rf) relative to the axis; - a push rod (80) able to push the discs against each other on a thrust surface (4) in a direction parallel to the axis, the thrust surface having an average thrust radius (Rp) relative to the axis, which extends within or beyond the average friction radius (Rf). The push rod (80) has a radial annular notch (90) which recesses the push rod from the side of the push rod opposite the axis (O-O) and not from the side of the push rod closest to the axis, when the average thrust radius (Rp) extends beyond the average friction radius (Rf).

Description

TECHNICAL FIELD

[0001] The present invention relates to hydraulic machines, but in particular not only to hydraulic machines with radial pistons. PRIOR ART

[0002] Many types of hydraulic machines have been proposed. One embodiment of this type of machine will be reproduced in Figure 1 and Figure 2 . It mainly comprises five components: a housing 10, a shaft 20, a component forming a motor or pump between the housing and the shaft 30, bearings or rolling element bearings 42, 43 for guiding the rotation of the shaft relative to the housing, and a brake 49.

[0003] The housing 10 is intended to be attached to the chassis of a machine or vehicle. It comprises a cam 12 with a plurality of lobes, clamped between two side elements of the housing.

[0004] The shaft 20 supports a power take-off 28, which is adapted to carry an accessory that must be driven in rotation, for example, in the case where the machine constitutes a motor and delivers a driving torque to the accessory, which is a wheel member or any other mechanical rim. In the case where the machine constitutes a pump, the power take-off receives the torque of a driving mechanical motor applied to the inlet of the machine.

[0005] The component forming a motor or pump 30 has radial pistons. It comprises a distributor 32, a cylinder block 34 comprising a plurality of radial cylinders 35 each housing a piston 36, each piston carrying a roller 38 abutting against the cam 12 integral with the housing. When the distributor 32 cyclically places the fluid under pressure within the cylinders 35, the force acting on the associated rollers 38 and pistons 36 on the cam 12 drives the cylinder block 34 in rotation relative to the cam, and thus relative to the housing 10.

[0006] The cylinder block 34 is in rotation with the central element 22 of the shaft, which in this case is driven in rotation by the pressure of the fluid applied by the distributor. The hydraulic machine thus constitutes a motor.

[0007] Conversely, when the power take-off exerts a mechanical force on the shaft 20 in the direction of rotation relative to the housing 10, the movement of the rollers and pistons relative to the lobes of the cam causes a variation in the volume of the cylinders and thus exerts a fluid pressure on the distributor. The machine then acts as a pump.

[0008] This machine is reversible and thus can work like a pump or a motor, but also can turn in both rotation directions. Thus, this type of hydraulic machine can be found in four different cases, which define four quadrant values of pressure and flow direction: forward movement in traction or in holding, and backward movement in traction or in holding.

[0009] The braking portion 49 is formed by a stack of alternately rotating abutting discs, some of which are connected to the shaft and others of which are connected to the housing. These discs abut against each other by means of elastic elements 56, such as Belleville washers, and are thus in the braking position.

[0010] This member 56 is arranged between, on the one hand, an element of the housing and, on the other hand, the longitudinal piston 51 abutting against the stack of discs. A force opposite to the elastic member can be applied in a control chamber 58 placed between the stack of discs and the piston in order to place the braking portion in the unbraking position.

[0011] It is important here to distinguish between the friction surface or the rubbing surface of the discs. This is the surface of the discs by which they come into contact with each other and generate the friction that produces the braking. It must therefore be distinguished from the surface of the discs that does not provide this friction. It is also important to distinguish the thrust surface, which is the surface of the longitudinal piston 51 and of the first disc of the stack, by which these two members come into contact with each other in order to transmit the thrust.

[0012] In many machines, the friction surface and the thrust surface do not coincide when viewed in their respective planes perpendicular to the axis. In other words, they are not locally centred with respect to each other (although the longitudinal piston and the discs are coaxial). This is the case, for example, when the friction surface is offset in the radial direction opposite to the axis with respect to the thrust surface. In some cases, the opposite is observed. In other words, this is a case of non-coincidence of the respective radial positions of the friction surface and of the thrust surface, the friction surface being able to be radially higher than the thrust surface and the case being able to be the opposite.

[0013] In both cases, this indicates that the thrust of the piston is not applied in alignment with the maximum part of the friction surface or is not properly locally centred with respect to the friction surface. As a result, the thrust is not optimally transmitted to the discs, resulting in an uneven contact pressure of the friction surface. As a result, the thrust is poorly distributed in the discs, in particular in certain places. Possible consequences are the appearance of a tendency to excessive torque or jamming. Excessive torque is defined as an additional torque that is provided temporarily and whose intensity cannot be predicted. For example, two braking portions mounted on the same shaft can exhibit considerable differences in torque, resulting in instability of the machine during braking. It is also possible to see vibrations appear. Compensation for this results in the dimensions of the group of parts through which the braking torque passes being too large. For example, the discs forming the braking portion need to be thicker in order to allow the additional torque in the splined connection of these discs with their respective opposite parts to pass. However, both of these cases are to be avoided. By way of example, braking portions with discs that are nitrided are particularly susceptible to excessive torque.

[0014] An object of the invention is to avoid oversized dimensions of the components of the transmission chain of the braking torque (in particular, to avoid increasing the thickness of the discs, their diameter and the number of their splines) and to reduce the risk of excessive torque or machine jamming. SUMMARY

[0015] To this end, a hydraulic machine is provided, comprising: - a fixed part, - a part rotatably mounted relative to the fixed part about an axis, - a stack of discs forming a braking portion or a clutch, said discs being able to abut against each other by friction surfaces, said friction surfaces having an average friction radius measured from the axis, - a push rod able to push said discs against each other on a push surface in a direction parallel to the axis, said push surface having an average push radius measured from the axis and extending within or beyond the average friction radius, the push rod having a radial annular notch recessing the push rod from a side of the push rod opposite the axis, rather than from a side of the push rod closest to the axis, when the average push radius extends beyond the average friction radius.

[0016] In other words, the notch is positioned on the side of the gap between the position of the application of the push force and the average radius of the friction surfaces of the discs. Thus, in the event of a misalignment between the friction surfaces and the push surface, the notch allows the push rod to bend in order to recenter the push force on the friction surfaces. Thus, the push force is applied more perpendicularly to the friction surfaces. For example, if the pressure on the side closest to the outside of the stack of discs is too great, the presence of the notch allows this part to be relieved. Thus, the pressure distribution is more uniform. Since there is no strong contact pressure, the so-called "dry" lubrication state (i.e. the state of excessive torque) is avoided. The braking is better and more regular. Furthermore, there is no longer a need for oversized dimensions of the transmission components of the braking torque chain. In short, the invention allows the push force to be better distributed on the stack of discs in order to avoid the phenomena of jamming and excessive torque. Furthermore, this solution implements a single part, rather than several parts movable relative to each other, to simplify assembly and manufacturing, in particular to reduce the risk of missing a part during assembly of the machine.

[0017] It can be observed that the notch extends in the part of the push rod that transmits the push force to the discs.

[0018] It can be provided that the bottom of the notch extends adjacent to the push surface. In other words, the radius of the notch at the bottom of the notch is between the smaller radius of the push surface and the larger radius of the push surface.

[0019] It can be provided that the bottom of the notch extends adjacent to the friction surface. In other words, the radius of the notch at the bottom of the notch is between the smaller radius of the friction surface and the larger radius of the friction surface.

[0020] It can be provided that the machine is configured so that the member exerts a braking force on the push rod on a receiving area having an average receiving radius measured from the axis and that the average receiving radius extends beyond the average thrust radius when the average thrust radius extends beyond the average friction radius, rather than within the average thrust radius.

[0021] It can be provided that the receiving area has a smaller radius that extends beyond the larger radius of the thrust surface or the friction surface, rather than within the larger radius of the thrust surface or the friction surface, when the average thrust radius extends beyond the average friction radius.

[0022] It can be provided that the receiving area has a smaller radius that extends beyond the smaller radius of the recess, rather than within the smaller radius of the recess, when the average thrust radius extends beyond the average friction radius.

[0023] It can be provided that the push rod has a larger radius than the larger radius of the friction surface.

[0024] In this configuration, in an axial view of the machine, the push rod has a dimension that exceeds the friction surface of the stack of discs. The push rod has a radius that is located outside the friction surface.

[0025] Preferably, the recess is sized so that the average friction radius is between the larger radius of the recess and the smaller radius of the recess.

[0026] Thus, the recess extends up to the average radius perpendicular to the friction surface.

[0027] It can be provided that the larger radius of the friction surface is greater than the smaller radius of the recess, or that the smaller radius of the friction surface is smaller than the larger radius of the recess.

[0028] It can be provided that the machine is arranged so that at least a portion of the push rod gradually bends as the thrust of the push rod against the stack increases.

[0029] Thus, this bending allows to reduce the contact pressure in the area of the thrust surface that is not suitably centered with respect to the friction surface. This portion of the push rod can be closest to the stack or farthest from the stack.

[0030] In one embodiment, the axial dimension of a portion of the push rod decreases in the direction of the free end of the portion.

[0031] This configuration allows to control the deformation of this deformable portion of the push rod and thus the distribution of the contact pressure. This portion of the push rod can be closest to the stack or farthest from the stack.

[0032] It can be provided that the recess has two main faces facing each other, one of these faces being oriented obliquely towards the outside of the push rod.

[0033] This oblique face facilitates the bending of the push rod. Furthermore, it facilitates the machining of the bottom of the recess, if necessary, by simplifying the access to it.

[0034] Advantageously, the oblique face of the recess extends from the side closest to the stack.

[0035] This arrangement constitutes a means of producing the deformable portion of the push rod while still controlling the deformation and development of the contact pressure.

[0036] It can be provided that the push rod has a push rod guide face in the axial direction relative to the support.

[0037] Preferably, the guide face extends entirely from the side of the recess furthest from the stack.

[0038] Thus, within the push rod, there is no interference between the zone designated to deform upon pushing and the zone used as a guide.

[0039] It can be provided that the machine comprises a calibration spring able to push the push rod against the stack.

[0040] This means that, in the absence of other loads, the spring provides a constant braking load. The dimensions of the recess can then be determined as a function of this intensity, to obtain the desired stress distribution. Thus, if necessary, the dimensions of the bending of the part can be determined.

[0041] The machine can also have at least one of the following characteristics:

[0042] - it comprises a spring able to push the push rod against the stack, and a deactivation chamber, the deactivation chamber being arranged so that the hydraulic pressure in the chamber exerts a force on the spring opposing the braking;

[0043] - the stack is in an oil bath;

[0044] - the disc is made of nitriding steel;

[0045] - the disc comprises an inner lining of friction material;

[0046] - the inner lining has grooves; and

[0047] - the stack forms a brake or a clutch.

[0048] Thus, if necessary, these grooves can be used to pass the oil.

[0049] If necessary, a braking portion can be provided to provide at least one of the functions of a motor, an emergency braking portion, a safety braking portion (so that, in the event of a machine malfunction, the braking portion immobilizes it) and a parking braking portion. BRIEF DESCRIPTION OF DRAWINGS

[0050] We will now present, by way of non-limiting examples, embodiments of the application with reference to the appended drawings, in which:

[0051] - Figure 1 is an axial section view of a machine according to the prior art;

[0052] - Figure 2 is a transverse section view of the machine along the plane II-II of Figure 1 ;

[0053] - Figure 3 is a view of the machine according to one embodiment of the application;

[0054] - Figure 4 and Figure 5 are different axial views, mainly showing Figure 3 the push rod of the machine shown in , and showing the features of the push rod; and

[0055] Figure 6 - Figure 7 show the facilities for the forces in the stack of the push rod and the disc of the machine for the numerical simulation Figure 3 , and the observed pressure values. DETAILED DESCRIPTION

[0056] As for the machine of Figure 1 and Figure 2 , Figure 3 and Figure 4 the hydraulic machine 2 according to the present embodiment of the machine shown in is centered on an axis O-O and essentially comprises five complementary assemblies: a housing 10, a shaft 20, an assembly forming a motor or a pump (not shown and located between the housing 10 and the shaft 20), means forming a bearing for guiding the relative rotation of the shaft 20 with respect to the housing 10, not shown, and a braking portion 49.

[0057] The housing 10 is intended to be attached to the chassis of a machine or vehicle. It comprises a cam (not shown) with a plurality of lobes, which is clamped between two side elements of the housing.

[0058] The shaft 20 supports a power take-off adapted to carry an accessory that must be rotationally driven in rotation, for example, in the case where the machine constitutes a motor, a wheel or any other mechanical rim. In the case where it constitutes a pump, the power take-off receives the mechanical motor torque applied to the inlet of the machine.

[0059] The components forming a motor or pump have radial pistons. They mainly include a distributor and a cylinder body, the cylinder body comprising radial cylinders housing the respective pistons, each radial cylinder carrying rollers that abut against a cam integral with the housing. The number of cylinders and the number of pistons in the cylinder body differs from the number of cam lobes. As in... Figure 1 and Figure 2 In the machine, the cam is radially external, and the cylinder block, radially internal to the cam, has a cylinder that opens radially outward toward the cam. The distributor is powered via an element that forms a cover and connector for supplying power to the distributor.

[0060] In a manner known per se, when the distributor circulates pressurized fluid within the cylinder, the load on the associated rollers on the piston and cam drives the cylinder to rotate relative to the cam, and thus relative to the housing. The cylinder is rotatably connected to the central element of shaft 20 via a system of longitudinal splines, the shaft being rotated by the pressure of the fluid. In this case, the machine constitutes a motor. Conversely, when the power take-off applies mechanical force to shaft 20 in a drive direction of rotation relative to housing 10, the movement of the rollers and piston relative to the cam's lobes causes a change in the cylinder's volume, and thus applies fluid pressure to the distributor. The machine then functions as a pump. This machine is reversible, and therefore can operate like a pump or motor, and can rotate in both directions of rotation.

[0061] To limit the axial volume of the machine, the power take-off unit can be located outside the radially external components, such as... Figure 3 As shown in the example. According to a variant embodiment, the power take-off device is axially positioned on a disc transverse to the axis OO, as... Figure 1 The situation is shown.

[0062] Figure 3 The diagram shows a stationary portion associated with housing 10 and a rotating portion including shaft 20. The bearing assembly (not shown) comprises two rolling element bearings, with rollers inserted between shaft 20 and housing 10.

[0063] The shaft 20 has a central region or hub 22 that is truncated by the axis OO and a cylindrical extension 24 that is away from the axis. The cylindrical extension forms a ring gear and is connected to the central region by a connecting disc 16.

[0064] The housing 10 has a cylindrical axial extension 11.

[0065] Braking unit 49 is a disc brake type. It is formed by stacks 52 and 54 of discs that are rotated alternately, some of which are connected to shaft 20 and others to housing 10. Thus, the discs are alternately connected in space to the stationary part 10 and the rotating part 20 along the longitudinal axis OO.

[0066] Each disc 52, 54 is formed by a washer. Their respective rotation connection with the housing and the shaft can be formed, for example, by engaging ribs provided on the radial outer periphery or, alternatively, on the radial inner periphery of the discs 52, 54 into complementary splines or grooves formed facing the ribs on the extension 11 of the housing and on the ring gear 24 of the shaft 20 respectively associated.

[0067] The machine has a brake chamber 55 placed axially opposite the cylinder with respect to the stack of discs. Thus, in Figure 3 , the brake chamber is located on the right of the stack. In this case, the brake 49 is arranged at the axial end of the machine adjacent to the power take-off, i.e. close to the power take-off, opposite the distributor with respect to the cylinder.

[0068] What is called "proximal" here is the part of the brake piece 49 oriented towards the formation of the assembly of the motor or pump, thus to the left in Figure 3 , while "distal" is the part of it oriented inversely, to the right in the figures, away from this assembly, towards the outside of the machine.

[0069] Furthermore, as with the axial extension 11 of the housing 10, the brake chamber 55 is in this case inserted in the radial direction between the central region 22 of the shaft 20 and the ring gear 24.

[0070] The stack 50 of discs is again placed between two axial supports. One is similar to Figure 1 the support 17, not shown in Figure 3 . The other is a push rod 80, which will be described below. Elastic elements 56, for example of the Belleville washer type, act in a mutually abutting manner on the alternating discs, thus in the braking position. In this case, the concave face of the Belleville washers is directed towards the stack 50. According to the embodiment shown, the Belleville washers abut against the longitudinal annular piston 51 acting on the stack 50 during braking, preferably on its radial periphery.

[0071] On the side of the spring opposite the piston in the axial direction, a stop ring 85 is associated with the spring 56, which is housed in an annular recess of the extension 11, and a wedge 89 is inserted between them in the axial direction. The ring and the wedge ensure the axial blocking of the edge of the spring closest to the axis O-O.

[0072] A force opposite the elastic member 56 can be applied in a control chamber or debraking chamber 58 located between the stack 50 of discs and the longitudinal piston 51 in order to place the brake 49 in the debraking position. The piston 51 delimiting the debraking chamber 58 is movable by sliding with respect to the housing 10 along the axis O-O.

[0073] It comprises a portion forming a cylindrical sheath 62 which is inserted in the axial direction between the stack 50 of discs and the spring 56. The sheath 62 extends through a portion in the form of a washer 64 which is transverse to the axis O-O, associated with a gasket 68 relative to the extension 11 to constitute a wall of the deactivation chamber 58. The sheath 62 serves as a loading element abutting against the stack 52, 54 of discs at its proximal end. The parts 62 and 64 are assembled to one another in a rigid and sealed manner, for example by screwing and by incorporating static sealing means such as a seal, or are a single block as illustrated. The piston 51 thus has an "L" shaped half-section, with a branch 64 transverse to the axis and a longitudinal branch parallel to the axis, corresponding to the sheath 62. The piston 51 is thus able to exert a force against the brake on the spring 56 when pressure is exerted in the deactivation chamber 58 to inflate it. Other forms of positioning and cooperation between the piston 51 and the spring 56 are possible.

[0074] The machine comprises a ring 70 transverse to the axis O-O which is placed between the stack 50 of discs and the washer 64 of the piston. The ring 70 forms one of the transverse walls of the deactivation chamber 58. The ring is housed in the radial direction between the sheath 62 and the extension 11 facing the ring, and has a clearance for sliding relative to the piston 51, i.e. a radial dimension which is less than the radial clearance existing between these parts, to allow at least slight axial relative movement between the ring 70 and the piston 51. The ring 70 is associated with two seals 72, 74 which cooperate respectively with the piston 51 and the housing element 11. The sheath portion 62 is able to slide relative to the ring 70.

[0075] The deactivation chamber 58 thus has an annular shape and is delimited in the axial direction by the piston washer 64 and the ring 70, and in the radial direction by the sheath 62 and the extension 11.

[0076] The deactivation chamber 58 is closed by three seals 68, 72 and 74.

[0077] The seal 68 associated with the piston 51 is of the type known as "joint D ring" in accordance with standard DIN 11850, comprising a semicircular face and a flat face. This seal is housed in a complementary width groove, which is preferably formed in the washer 64, or, as a variant, in the element 11 of the housing placed facing the gasket. The flat face of the seal 68 is placed on the bottom of the groove. The semicircular face of the seal rests against a surface element which is able to translate relatively along the axis O-O.

[0078] In this case, the seal 72 which provides sealing between the ring 70 and the piston 51 is of the same type.

[0079] The seal 74, which provides a seal between the ring 70 and the element 11 of the housing 10 placed facing the ring, is preferably an O-ring seal, or a "D-ring" D-shaped ring. As illustrated, the use of a D-ring allows the seal to be handled well during assembly when it is placed on the washer 70.

[0080] The deactivation chamber 58 is supplied by means of at least one at least partially longitudinal passage 13, formed in the extension 11 of the housing, which opens into the chamber 58. Without being limiting, the passage 13 can for example open at a step formed on the periphery of the longitudinal extension 11, as illustrated. Figure 3 The passage 13 is connected to a deactivation control line of the hydraulic machine.

[0081] The push rod 80 is inserted in the axial direction between the stack 50 of discs and the ring 70.

[0082] Thus, in the axial longitudinal direction, from proximal to distal, the machine comprises in particular:

[0083] - the stack 50 of discs,

[0084] - the push rod 80 which directly axially abuts the first disc of the stack,

[0085] - the ring 70 which directly axially abuts the push rod 80,

[0086] - the sheath 62 which itself surrounds the ring 70 and which also directly axially abuts the push rod 80,

[0087] - the deactivation chamber 58,

[0088] - the gasket 64 of the piston 51,

[0089] - the spring 56,

[0090] - the wedge 89, and

[0091] - the stop ring 85.

[0092] The wedge 87 is inserted in the axial direction between the shoulder of the extension 11 of the housing and the part of the ring 70 closest to the axis.

[0093] In rest, the spring 56 acts on the sheath 62 and on the push rod 80 which axially abuts the stack 52, 54 of discs, and thus on the discs which abut each other. The braking portion 49 is then in the braking position. The shaft 20 is rigidly fixed relative to the housing 10.

[0094] On the other hand, assuming that fluid pressure is applied in the deactivation chamber 58 and generates an axial force opposite to the spring 56 and greater than the braking force generated by the spring. Because the axial abutment 87 limits the movement of the ring 70, the increase in the volume of the deactivation chamber causes the piston 51 to move in the direction of the spring 56, thus causing the free space of the spring between the piston 51 and the wedge 89 to decrease, thus cancelling the force exerted by the spring 56 on the stack of discs 52, 54 in the braking position. The stack of discs is no longer in abutment with each other, the braking portion 49 is placed in the deactivation position. The shaft can rotate with respect to the housing.

[0095] Before describing the details of the pusher 80, it is important to emphasize that the general structure of the machine has been given by way of example and that a very large number of other configurations are possible. Thus, this configuration of the machine and its different features are not related to the invention. They only belong to this embodiment. For example, the present invention is compatible with the general configuration of the prior art machines of Figure 1 and Figure 2 .

[0096] With particular reference to Figure 3 and Figure 4 , the wedge 80 has a substantially annular shape. It has a flat annular proximal face 82 perpendicular to the axis O-O and capable of being in axial contact with the first disc 54 of the stack. On this face, on the one hand, an annular thrust area 84 capable of effectively coming into contact with the disc, on the other hand, an inert or non-effective area 86 which, when the thrust is applied, does not come into contact with the disc. Unlike the inert area 86, the thrust area 84 faces the disc.

[0097] The thrust area 84 has an average radius R p measured with respect to the axis. Here, the average is calculated as the arithmetic mean of the extreme radii of the thrust area, i.e. the smallest R m and the largest R1. Other calculation modes are also possible, for example by considering the integral of the radii of the thrust area.

[0098] The discs 52, 54 are capable of abutting against each other by means of friction surfaces. Thus, in the same way, it is possible to distinguish on each disc an annular friction area 88 capable of effectively coming into contact with the adjacent disc in the braking position and an inert or non-effective area 79 which, in the braking position, does not come into contact with the disc. Unlike the inert area 79, the friction area 88 is positioned facing the adjacent disc.

[0099] The friction area 88 has an average radius R f with respect to the axis. Here, the average is also calculated as the arithmetic mean of the extreme radii of the friction area, i.e. the smallest R2 and the largest R1. Other calculation modes are also possible, for example by considering the integral of the radii of the area.

[0100] The discs 52 directly engaged with the ring gear 24 are identical to each other. Likewise, the discs 54 directly engaged with the housing 10 are identical to each other. Since the friction areas 88 of all discs coincide in axial direction, the average radius R f is identical throughout the stack.

[0101] In Figure 3 the illustrated configuration, the average thrust radius R p extends beyond the average friction radius R f . In other words, the average thrust radius is greater than the average friction radius. This means that the thrust area 84 of the push rod 80 is offset in radial direction opposite to the axis O-O relative to the friction area 88.

[0102] Here, it can also be observed that the push rod 80 has a larger radius R M measured at its back face in contact with the sheath and at its outer cylindrical face, which is larger than the larger radius R1 of the friction surface 88. However, the front face 82 of the push rod here also has a radius R a which is larger than the larger radius R1 of the friction surface 88. The front face of the push rod further has a smaller radius R m which is larger than the smaller radius R2 of the friction surface 88.

[0103] Considering that the average thrust radius R p here extends beyond the average friction radius R f , the push rod 80 has an annular radial recess 90 which is recessed into the push rod from the circumference side of the push rod opposite to the axis O-O. The recess has a generally annular shape and extends generally along a plane perpendicular to the axis. The recess 90 extends in a portion of the push rod which transmits the thrust to the discs.

[0104] Here, the recess has a "U" shaped profile in circumferential direction and has two main faces 91, 92 facing each other. The back face 92 is flat and perpendicular to the axis.

[0105] The recess extends for example beyond half of the total thickness of the push rod measured in radial direction. However, it can also extend to two thirds, or even three quarters of this dimension, and takes any value comprised between these limits, including these limits.

[0106] In this case, the dimensions of the recess 90 are such that the average friction radius R f is comprised between the larger radius R a of the recess and the smaller radius R e of the recess. Thus, the bottom of the recess here extends up to the average friction radius R fAt the end, and slightly beyond the average friction radius in the radial direction of movement toward the axis.

[0107] Therefore, the notch 90 defines the front portion 81 and the rear portion 83 of the push rod 80. The front portion can contact the stack 50, while the rear portion cannot contact the stack, but in this configuration, it can contact the ring 70.

[0108] Relative to the axis, the bottom of the notch 90 extends adjacent to the thrust region 84. In other words, the radius R of the notch at the bottom of the notch... e The smaller radius R included in the thrust region 84 m Between the larger radius R1 of the thrust region.

[0109] The bottom of the notch extends adjacent to the friction surface 88. In other words, the radius R of the notch at the bottom of the notch... e It is contained between the smaller radius R2 of the friction surface 88 and the larger radius R1 of the friction surface. In particular, the larger radius R1 of the friction surface 88 is larger than the smaller radius of the notch.

[0110] In this case, the radius R of the rear 83 M The radius R of its front part is greater than 81. a Specifically, the sheath 62 applies axial pressure in the larger radius portion of the rear 83, and this portion is the non-facing portion at the front 81 of the push rod.

[0111] The machine is configured such that the sheath 62 applies a braking force to the push rod 80 on the receiving area 78 of the push rod, the receiving area having an average receiving radius R. r ,like Figure 3 As shown and measured from the axis. When the average thrust radius R p Extending beyond the average friction radius R f At that time, the average receiving radius is greater than the average thrust radius R. p For example, the situation here.

[0112] In this case, the receiving area 78 has a small radius R. c This smaller radius is larger than the larger radius R1 of the thrust surface or friction surface. This smaller radius R... c It is also greater than the smaller radius R of the notch measured at the bottom of the notch. e .

[0113] Like most parts, the push rod 80 is made of metal. The notch 90 gives the push rod the possibility of bending in order to approach the free end of the front part 81 in the direction of the rear part 83 and / or to approach the free end of the rear part in the direction of the front part. This bending occurs when the push rod abuts against the stack 50 in the braking position. This bending is represented in a very exaggerated manner in solid lines in Figure 5 Fig. 6 compared with the unbent configuration represented in dashed lines. This figure shows by way of example the case where the free end of the front part 81 approaches the rear part 83, it being understood that the opposite case and combinations of the two movements are also possible.

[0114] In the bending example shown in Figure 5 Fig. 6, when the bending occurs, the part of the front part 81 closest to the free end bends first and more than the rest of this front part. This bending allows the contact pressure on a portion of the contact surface to be reduced. It also allows the contact pressure to be distributed in a determined manner. Thus, the thrust surface 84 of the stack 50 against the disc tends to decrease so that the thrust surface becomes the part closest to the axis O-O. In particular, the thrust exerted by the push rod 80 on the stack of discs tends to concentrate on the part of the thrust surface 84 closest to the axis in order to be more consistent with the friction surface 88. This load distribution thus compensates for the difference between the average thrust radius R p and the average friction radius R f .

[0115] This bending shows the effect of the notch 90 which creates a weakening of the push rod 80 tending to bring the eccentric force on R M back around the radius R e . The force then spreads towards the surface 84, concentrating at R e . This spreading is a function of the thickness of the front part 81, denoted e. This thickness, determined correctly, ensures that the pressure F spreads in the most uniform manner possible.

[0116] Ideally, the contact surfaces 82 and 88 are congruent. In other words, R m = R2; R a = R1, so that R f = R p .

[0117] The push rod 80 has a guide face 96 for sliding the push rod in the axial direction relative to the support, here formed by the shoulder 98 of the ring 70. To this end, the shoulder of the ring has a cylindrical face 100 which makes surface contact with the face 96. The guide face 96 ensures that the push rod is centred in the machine.

[0118] As Figure 4As shown, the guiding face 96 extends completely from the side of the recess 90 furthest from the stack, i.e. on the rear distal portion 83. Thus, any risk of interference with the guiding function during propulsion and bending in braking situations is avoided. In Figure 3 and Figure 5 the illustrated pusher does not show this feature.

[0119] It can be observed that the contact pressure is transmitted from the piston 51 to the stack only by means of the pusher 80, which constitutes a rigid assembly that can be formed as a single piece.

[0120] As a variant, in the opposite case, the thrust surface 84 has an average thrust radius R p extending inside the average friction radius R f . In other words, the average thrust radius is smaller than the average friction radius. This means that the thrust area of the pusher 80 is offset in the axial direction with respect to the friction area 88.

[0121] Moreover, independently of this aspect, it can be seen from Figure 4 that one of the main faces 91 of the recess 90 is inclined to be oriented in the direction towards the outside of the pusher. Here this is the front proximal face, thus on the side of the stack 50 on the piece 81. This inclination facilitates access to the bottom of the recess during production of the latter, in particular by machining.

[0122] As for the face extending on the side of the recess closest to the stack, and because the thrust face 84 is flat, the proximal portion 81 of the pusher closest to the stack has an axial dimension e that decreases in the direction of the free end of this portion. This dimension is shown in particular in an enlarged manner in Figure 4 . Thanks to this arrangement, in this example, the portion 81 gradually bends as the pressure of the pusher against the stack increases. Thus, this arrangement allows good control of the amplitude of the bending as a function of the thrust.

[0123] But another portion 83 of the pusher can have a similar shape to obtain the same properties on this other portion (with or without this configuration of the proximal portion 81).

[0124] Thus, the pusher 80, which forms a wedge, has an optimized shape for diffusing and distributing the contact pressure into the stack of the disc.

[0125] Figure 6 and Figure 7 This is shown by the figures, which show a numerical simulation of the distribution of forces in the machine. In this simulation, only the sheath 62, the pusher 80, the stack 50, shown here as a single block, and the wedge 17 located on the other side of the stack are taken into account. Here, the pusher 80 has a shape similar to that shown in Figure 3The same construction, the recess 90 is recessed from the side of the push rod furthest from the axis.

[0126] These two figures illustrate the distribution of the forces in the stack of discs. It can be seen that this distribution is still good. In fact, the pressure generated at the contact interface between the sheath 62 and the push rod 80 is close to 6 MPa. This is the same as the pressure present at the entire intermediate portion of the push rod 80, in particular at the bottom of the recess 90 and up to the contact interface with the stack 50. On the other hand, inside the stack, the local pressure drops very quickly as one moves away from the push rod, presenting values of between 3 and 4 MPa, or even less. Thus, in this example, the pressure generated on the sheath side drops by 2 MPa once the pressure is transmitted into the stack. Moreover, the average pressure measured inside the stack remains relatively constant. Thus, a good compromise is achieved between, on the one hand, the distribution of the contact pressure in the stack of discs and, on the other hand, the mechanical resistance of the push rod and the mechanical processing constraints.

[0127] The stack 50 of discs is in a lubricating and cooling bath. The discs are made of, for example, nitrided steel. They can be equipped with an inner lining of friction material, which is, for example, grooved to allow the passage of oil between the discs. Thus, for the same reasons, the discs can comprise perforations or through grooves.

[0128] Of course, numerous modifications can be made to the application without departing from the scope of the application.

[0129] For example, the stack of discs can be used as a clutch in a rotating machine.

[0130] The guidance of the push rod 80 can be achieved by means of the face of the push rod directed in the opposite direction to the axis.

Claims

1. A hydraulic machine (2) comprising: - a fixed part (10), - a part (20) rotatably mounted about an axis (O-O) relative to said fixed part, A stack (50) of disc members (53, 54) forming a brake or clutch, said disc members being abuttable against each other by friction surfaces (88) having an average friction radius (R f ) measured from said axis of rotation, and a push rod (80) capable of pushing the discs against each other abutting against a thrust surface (84) in a direction parallel to the axis, the thrust surface having an average thrust radius (R p ) measured from the axis and extending within the average friction radius (Rf) or beyond the average friction radius (Rf), The push rod (80) has a radial annular recess (90) which indents the push rod from the side of the push rod opposite the axis (O-O) when the average push radius (Rp) extends beyond the average friction radius (Rf) and otherwise indents the push rod from the side of the push rod closest to the axis, wherein the recess (90) is sized such that the average friction radius (Rf) is between the larger radius (Ra) of the recess and the smaller radius (Rb) of the recess. e ) 2. The machine of claim 1, wherein, The radius (R) of the push rod (80) a R M The radius (R1) is greater than that of the friction surface.

3. The machine of claim 1, wherein, - said machine being arranged so that at least one portion (81, 83) of the push rod (80) is progressively bent as the push force of the push rod against the stack increases.

4. The machine of claim 1, wherein, - at least one portion (81) of the push rod (80) has an axial dimension (e) that decreases in the direction towards the free end of the portion.

5. The machine of claim 1, wherein, - said notch (90) has two main faces (91, 92) facing each other, one of these main faces being obliquely oriented in the direction towards the outside of the push rod.

6. The machine of claim 5, wherein, - said obliquely oriented main face extends from the side of the notch (90) that is closest to the stack (50).

7. The machine of claim 1, wherein, - said push rod (80) has a push rod guide face (96) in the axial direction relative to the support (70).

8. The machine of claim 7, wherein, - said push rod guide face (96) extends completely from the side of the notch (90) that is farthest from the stack (50).

9. The machine of claim 1, comprising: - a spring (56) able to push the push rod (80) against the stack, and - an unblocking chamber (58) arranged so that the hydraulic pressure in this chamber exerts a force against the spring that opposes the braking.

10. The machine of claim 1, wherein, - said stack (50) is in an oil bath.

11. The machine of claim 1, wherein, - said discs (52, 54) are made of nitriding steel.

12. The machine of claim 1, wherein, - said discs (52, 54) comprise an inner lining of friction material.

13. The machine of claim 12, wherein, - said inner lining has grooves.

14. The machine of claim 1, wherein, - said stack (50) forms a braking portion.

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