WO2021123549A1

WO2021123549A1 - Hydraulic machine comprising a brake release member

Info

Publication number: WO2021123549A1
Application number: PCT/FR2020/052302
Authority: WO
Inventors: Julien René ENGRAND; Gilles Grillon; Dominique Pascal COSTAZ; Loïc BONNARD; Jérémy Gérard RESPECTE
Original assignee: Poclain Hydraulics Industrie
Priority date: 2019-12-20
Filing date: 2020-12-07
Publication date: 2021-06-24
Also published as: FR3105309B1; FR3105309A1

Abstract

The hydraulic machine (2) comprises: - a housing (4), - a shaft, - a cam, - a cylinder and piston block designed to cooperate with the cam, and - a brake (112), the brake comprising: - a stack of discs (20) connected alternately to the housing and to the shaft, - a spring (22), - a pusher (26) loaded by the spring to press the discs together, and - a first wall (132) and a second wall (134) interposed between the spring and the discs with reference to an axial direction (X-X) of the shaft and delimiting a chamber (24) with the pusher such that, when a liquid pressure in the chamber exceeds a predetermined threshold, the pusher moves against the spring. The first wall (132) is interposed between the spring and the second wall with reference to the axial direction and mounted so as to be able to move relative to the housing. The machine comprises a stop (38) limiting the travel of the first wall (132) towards the spring such that the first wall remains at a distance from the spring. The machine is arranged such that the pusher (26) comes to bear against the second wall (134) when the pusher moves against the spring.

Description

Hydraulic machine comprising a brake release member

FIELD OF THE INVENTION

The invention relates to hydraulic machines, in particular, but not exclusively, to hydraulic machines with radial pistons.

STATE OF THE ART

Many types of hydraulic machines are known. An exemplary embodiment of such a machine can be found in document FR-2 796 886. This machine essentially comprises five parts: a housing, a shaft, an assembly forming a motor or pump arranged between the housing and the shaft, bearings. guide for relative rotation of the shaft relative to the housing, and a brake.

The box is intended to be fixed to the frame of a machine, a vehicle or a machine. It includes a multi-lobe cam sandwiched between two side members of the housing. The shaft supports a power take-off adapted to carry an accessory which must be driven in rotation, for example the rim of a wheel or any other equipment, in the case where the machine constitutes an engine. In the case where it constitutes a pump, the power take-off receives a mechanical engine torque applied to the input of the machine.

The machine comprises an assembly of the motor type or radial piston pump. It essentially comprises a distributor, a cylinder block which comprises several radial cylinders each housing a respective piston each carrying a roller bearing against the cam integral with the housing. The number of cylinders and therefore of pistons differs from the number of lobes of the cam.

When the distributor cyclically applies a pressurized fluid inside the cylinders, the biasing of the pistons and the associated rollers on the cam causes the cylinder block to rotate with respect to the cam and therefore with respect to the housing. The cylinder block being connected in rotation to the shaft, the latter is driven in rotation by the pressure of the fluid applied by the distributor. The hydraulic machine in this case constitutes a motor. When, on the contrary, a mechanical force is applied by the power take-off on the shaft, the displacement of the rollers and of the pistons relative to the lobes of the cam induces a variation in the volume of the cylinders and consequently applies a fluid pressure on the distributor. The machine then operates as a pump. This machine is reversible, and therefore operates as a pump or a motor, and can also rotate in two directions of rotation.

The brake is of the disc brake type. It is formed by a stack of discs linked alternately in rotation, one to the shaft and the other to the housing. The discs are urged in mutual support, therefore in the braking position, by a spring, for example of the conical elastic washer type, generally referred to as the Belleville washer. The spring is arranged between, on the one hand, an element of the housing and, on the other hand, a piston or pusher which bears on the stack of discs. An antagonistic force to the spring can be applied to the plunger in a control chamber in order to allow the relative rotation of the shaft and the housing, that is to say in order to place the brake in the so-called brake release position.

The arrangement of this machine therefore makes it possible to limit its radial size while having a significant braking and brake release force.

In some machines of this type, the aforementioned spring biasing the pusher is locked in sliding by a resilient stop ring.

This ring bears against the internal edge of the washer and is itself rigidly fixed to an element of the housing, being blocked by a circlip received in a groove of the latter. This type of arrangement is provided when there is no solid part capable of serving as an axial stop for the washer.

This configuration has been proven and is relatively inexpensive. However, the force that this stop ring must withstand in a direction parallel to the axis of the machine depends on the configuration of the brake. In fact, in the braking position, the ring simply undergoes the force generated by the washer which bears on the pusher, itself bearing on the discs.

But in the brake release position, hydraulic pressure is exerted on the pusher in the direction opposite to the discs. It results in an axial stress transmitted from the pusher to the washer, then to the ring. From a certain pressure threshold, any increase in pressure results in a thrust directly transmitted to the ring. The stress to which the latter is subjected is therefore of much higher intensity, in particular of an intensity which may be excessively higher than what is necessary to compress the spring and obtain maximum brake release.

Under these conditions, the smaller the diameter on which the stop ring is installed, the lower the loads it can accept. The question of the sturdiness of the stop ring therefore arises if we reach high pressure for controlling the brake during release. The question of the holding of the stop ring is to be understood as also relating to the robustness of the groove which receives the ring. Designing a ring and a groove to receive it very robust makes the parts thicker, more cumbersome, and the operation of installing the ring difficult for operators. The reliability of such an assembly as a function of malfunctions on the maximum brake release pressure always remains limited by the dimensioning of the ring and of its groove.

An aim of the invention is therefore to reinforce the reliability of the machine, whatever the level of pilot pressure used in this configuration.

DISCLOSURE OF THE INVENTION

The invention solves this problem by limiting the stresses seen by the spring and its stopper.

For this purpose, according to the invention, a hydraulic piston machine is provided, comprising:

- a housing,

- a tree, - a cam,

- a cylinder and piston block able to cooperate with the cam, and

- a brake, the brake comprising: - a stack of discs connected alternately to the housing and to the shaft,

- a spring,

- a pusher biased by the spring to put the discs in mutual support, and

a first wall and a second wall interposed between the spring and the discs with reference to an axial direction of the shaft and delimiting a chamber with the pusher so that, when a liquid pressure in the chamber exceeds a predetermined threshold, the pusher moves against the spring,

. the first wall being interposed between the spring and the second wall with reference to the axial direction and movably mounted relative to the housing,

. the machine comprising a stop limiting a stroke of the first wall in the direction of the spring so that the first wall remains distant from the spring,. the machine being arranged so that the pusher comes to bear against the second wall when the pusher moves against the spring.

Thus, due to the presence of the stopper, the first wall does not bear directly against the spring, regardless of the pilot pressure used during the brake release. The spring stopper, such as a stopper ring, is thus protected against the stresses appearing during the brake release. The robustness of the machine is therefore preserved and the robustness of the assembly of the spring and of its stop piece is increased without modifying their dimensioning.

In addition, when the pusher comes to bear against the second wall, if the second wall is rigidly fixed to the housing, the stroke of the pusher in the direction of the spring is limited. Indeed, this wall then forms a stop for the pusher. This feature therefore provides security to protect the machine. Thus, the force to be exerted on the spring is limited beyond a threshold of the stroke of the pusher.

If, on the contrary, the second wall is mounted to be movable relative to the housing, once the pusher has supported on the second wall, they move with the first. However, the hydraulic pressure is exerted in the chamber on the two walls in different directions in the axial direction. It is therefore only the surface area exposed to the pressure without being compensated by a pressure in the opposite direction which generates a hydraulic stress on the assembly to move it further in the direction of the spring. In other words, as in the chamber the area of the second wall is smaller than that of the first, the thrust is exerted more effectively only on the area forming the difference of the areas so that the thrust is reduced. To continue to move the tappet during the brake release, it is therefore necessary to produce a higher hydraulic pressure. However, at this stage, brake release has already been obtained and there is no need to move the pusher further away from the discs. It is therefore not useful to generate a pressure so high that it would allow the movement to continue in the direction of the spring. This feature therefore provides security to protect the machine. Thus, for a given pressure in the chamber, the force exerted on the spring is reduced beyond a threshold of the stroke of the pusher. More particularly, the effective hydraulic thrust surface exerted on the spring is reduced, from a certain threshold of the stroke of the pusher.

Advantageously, the machine is arranged so that the pusher comes to bear against the second wall via a shoulder.

Thus, so that the pusher can come to bear against the second wall, the pusher has a shoulder which constitutes a contact surface intended to transmit the forces of the pusher to the second wall in the axial direction beyond a certain stroke when the pusher moves towards the spring. To form this shoulder, the pusher can be made in one or more parts.

In the case where the pusher and the shoulder are made in several parts, then the pusher and the shoulder are mechanically linked together so that at least part of the forces generated by the pusher beyond a certain stroke in the axial direction can be transmitted to the second wall by means of the part forming the shoulder.

By way of example, the mechanical connection binding in this case the pusher and the shoulder can be a built-in connection or a non-slip pivot connection.

Preferably, the second wall is mounted to move relative to the pusher.

Provision can be made for the stopper to be carried directly by the pusher. Thus, the stopper is not fixed but mobile. The first wall therefore comes to bear on the pusher.

Advantageously, the stop extends closer to a peripheral edge of the first wall than to an internal edge of the first wall.

Thus, the stopper can be given a relatively large diameter to enable it to withstand higher stresses than if the stopper were at the level of the internal edge of the first wall.

Provision can be made for the first wall to be rigidly fixed to the pusher, for example by being in one piece with the pusher. Alternatively, the first wall is mounted to move relative to the pusher.

Likewise, provision can be made for the second wall to be rigidly fixed to the housing.

Alternatively, the second wall is mounted to move relative to the housing.

There is also provided according to the invention a vehicle or a machine comprising at least one machine according to the invention.

DESCRIPTION OF FIGURES We will now present several embodiments of the invention and variants with reference to the appended drawings in which:

FIG. 1 is a partial sectional view of a hydraulic machine according to the invention;

Figures 2 to 4 are sectional views on a larger scale of the brake of the machine of Figure 1 showing a first embodiment of the invention in three respective stages of operation;

FIGS. 5 and 6 are curves illustrating the evolution of the stroke of parts and the evolution of certain stresses as a function of the pressure, in this embodiment and in a variant respectively; and FIGS. 7 to 9 are views similar to FIGS. 2 to 4 showing a second embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION First Embodiment

A first embodiment of the hydraulic machine according to the invention will now be described with reference to Figures 1 to 4.

We find in these figures a hydraulic machine 2 centered on an axis XX, which essentially comprises five complementary parts: a housing 4, a shaft or rotating part 6 mounted to be movable in rotation with respect to the housing 4 around the axis XX, an assembly 8 forming a motor or pump arranged between the housing 4 and the shaft 6, means 10 forming guide bearings for relative rotation of the shaft with respect to the housing, and a brake 112.

In what follows, the movements in the axial direction will be considered as taking place in a direction parallel to the X-X axis. Most of the parts of the machine have symmetry of revolution around this axis and therefore only visible in section in the figures.

Each of the five aforementioned parts 4, 6, 8, 10 and 112 can be the subject of numerous variant embodiments.

The housing 4 is intended to be fixed to the frame of a machine or of a vehicle. It preferably comprises a cam 14 with multiple lobes, not illustrated in detail and known per se, sandwiched between two side elements of the housing.

Shaft 6 carries a power take-off, not shown. The housing 4 and the cam 14 form the fixed part of the hydraulic machine which is connected to the frame of a machine, machine or vehicle, while the shaft 6 is linked to the object to be driven.

The assembly 8 of the radial piston motor or pump type is known per se and has not been shown in detail. It essentially comprises a distributor and its hydraulic supply, not shown in the figure, and a cylinder block 15 which comprises a plurality of radial cylinders 16 each housing a respective piston 18 each carrying a roller 19 bearing against the cam 14. integral with the housing.

The number of cylinders 16 and therefore of pistons 18 of the cylinder block preferably differs from the number of lobes of the cam 14. The cam 14 is preferably radially outer and the cylinder block, located radially inside the cam, has its cylinders 16 which open radially outwards, opposite the cam.

In a manner known per se, when the distributor cyclically applies a pressurized fluid inside the cylinders 16, the biasing of the pistons 18 and of the associated rollers 19 on the cam 14 causes the cylinder block to rotate relative to the cam and therefore with respect to the housing 4.

The cylinder block being connected in rotation with the central element of the shaft 6 by a system of longitudinal splines (not shown), the shaft is driven in rotation by the pressure of the fluid applied by the distributor. The hydraulic machine in this case constitutes a motor.

When, on the contrary, a mechanical force is applied by the power take-off on the shaft 6 in the direction of a rotational drive relative to the housing 4, the movement of the rollers and the pistons relative to the lobes of the cam 14 induces a variation in the volume of the cylinders and consequently applies a fluid pressure on the distributor. The machine then operates as a pump. The motor or pump assembly is only very schematically shown in Figure 1.

The means forming bearings 10 can be the subject of numerous embodiments. They preferably consist of two tapered roller bearings interposed between the shaft 6, for example a central element of the shaft, and an element 25 of the housing 4. The bearing means are only shown schematically in the figures, as this. or with regard to their structure and location.

The brake 112 is of the disc brake type. It is formed by a stack of discs 20 linked, in spatial alternation along the axial direction X-X, rotating one to the shaft 6 and the other to the housing 4.

The alternating discs are urged into mutual support, therefore in the braking position, here from the left in the figure, by a spring or elastic element 22, formed for example and preferably by a Belleville washer. This Belleville washer has its concavity directed towards the stack of discs in the illustrated embodiments.

The brake 112 comprises a pusher or piston 26 interposed axially between the spring 22, here on the left, and the stack of discs, on the right.

This pusher has an approximately cylindrical shape, the pusher being able to have various shapes. It is in contact by an axial end with the circumferential outer edge of the washer 22, on the left in FIGS. 1 and 2, and by its right axial end with the first disc 20 of the stack.

A fixed support 31 integral with the housing 4 is provided on the side of the stack opposite to the pusher 26 to ensure with the latter the compression of the stack during braking.

The spring 22 is immobilized on the internal element 25 of the housing by a stop ring 28 threaded onto this internal element, and itself locked in sliding manner by a circlip 30 inserted in a groove of the internal element 25. This arrangement therefore maintains the spring 22, at its internal end edge, in axial bearing against the pusher 26.

An axial force opposing the spring 22 can be applied in a control chamber or brake release chamber 24, located between the stack of discs and the spring, in order to place the brake 112 in the brake release position.

To this end, the brake comprises a first wall 132 and a second wall 134. These walls here each have shapes similar to those of flat discs hollowed out in their center and threaded onto the internal element 25 of the housing while being centered on the. axis XX. The walls are therefore located respectively in two planes perpendicular to this axis. They are here each mounted to slide relative to the housing element 25 and also relative to the pusher 26. Sealing gaskets 29 are mounted in the internal and external edges of these walls facing respectively the element 25 and the pusher 26 in the radial direction. The chamber 24 is therefore delimited in a sealed manner by the two walls 132, 134, the pusher 26 and the element 25. A duct 36 allows liquid under pressure to be conveyed into this chamber in a known manner. The duct 36 is not shown in full in the figure. It consists in a manner known per se of a drilled channel opening onto a non-rotating part of the machine, for example on the outer wall of the housing 4. This channel typically receives a connection to a brake release line, supplied by a hydraulic circuit. not shown which delivers brake release pressure on demand.

The two walls 132, 134 here even have the external diameter. However, the internal diameter of the first wall 132 is greater than that of the second wall 134. The latter is arranged on a step formed between two shoulders 27 and 40 of the element 25.

The sliding of the first wall 132 is limited in the axial direction, in the direction of the second wall 134, to the right in FIG. 2, by this second wall and by the shoulder 27 of the element 25 of the housing.

It is limited in the axial direction, in the direction of the spring, to the left in the figure, by a stop 138 formed in this case by a ring housed in a groove formed in a cylindrical face of the pusher 26 oriented in the direction of the axis. . The stop protrudes out of the groove, at a distance from the left axial end of the pusher and therefore prevents the first wall 132 from coming to bear axially against the spring. The axial sliding of the second wall 134 is limited in the direction of the first by the latter and in the opposite direction by the second shoulder 40 of the element 25.

The pusher 26 also has a shoulder 42 capable of coming into contact from the right in the axial direction with the second wall 134, at its part furthest from the axis.

In this embodiment as well as in all those shown, the pusher 26 and the shoulder 42 are made in one piece. One could nevertheless imagine that the pusher 26 and the shoulder 42 are produced by means of two separate mechanically linked parts.

The brake operates as follows.

At rest, with reference to FIG. 2, the washer 22 axially urges the pusher 26 which in turn urges the discs 20 of the stack to bear against each other. The shaft 6 is therefore immobilized with respect to the housing 4 in the braking position of the brake. The first wall 132 bears axially against the stop 138. The shoulder 42 of the pusher is spaced from the second wall 134.

When it is desired to rotate the shaft relative to the housing, the brake release chamber is supplied with pressurized liquid P via the conduit 36. The liquid pressure is applied over the entire surface Si of the face of the first wall 132 located in chamber 24 to stress this wall with a hydraulic force F _h = Si x P.

Referring to Figure 3, the pusher 26 therefore receives in the axial direction on the one hand the force F _h of the first wall to the left and on the other hand, in the opposite direction to the right, the force F _r exerted by the spring. As long as the intensity of the force F _h remains lower than that of the force F _r , the pusher remains stationary.

In figure 5, this is the part of the curves located between the pressure values A and B.

The curve “30/22; 22/26 ”in solid lines illustrates the evolution of the stress on the stopper 30 of the washer 22 by the latter and of the washer 22 by the pusher 26. The curve in dotted lines shows this evolution in the aforementioned machine of the prior art.

Likewise, the curve “134/26” shows the evolution of the stress on the second wall 134 by the pusher 26.

Curve “132 and 26” shows the movement of first wall 132 and pusher 26 with respect to the housing, and curve 134 that of the second wall.

During this first phase, the stress on the stopper 30 of the washer 22 by the latter and of the washer 22 by the pusher 26 remain at a constant non-zero level and all the other curves remain at the ordinate 0 .

When the force F _h exceeds the force F _r in intensity, the first wall 132, in direct axial bearing on the stop 138 and therefore in indirect bearing on the pusher 26, moves with the latter in the direction of the spring 22, against of the latter, to the left, until the shoulder 42 bears axially against the second wall 134. During this sliding of the pusher, it stops stressing the disks which therefore separate. The shaft can therefore rotate relative to the housing if the machine is controlled in this direction elsewhere. We are then in a brake release situation. During the movement of the pusher, the first wall 132 remains in abutment against the stop 138 and slides with the pusher. The second wall 134 remains stationary and the volume of the chamber 24 increases.

In figure 5, this is the phase between the pressure values B and C.

Thus the stress on the stopper 30 of the washer 22 by the latter and of the washer 22 by the pusher 26 increases.

The stress on the second wall 134 by the pusher 26 remains zero.

The curve “132 and 26” shows that the movement of the first wall 132 and of the pusher 26 with respect to the housing has started. But the second wall 134 remains stationary. Once the shoulder 42 is in contact with the second wall 134 as illustrated in Figure 4, the continued sliding of the pusher 26 can only be done by now also sliding the second wall so that the two walls 132, 134 slide together. Under these conditions, part of the force which made it possible to move the pusher no longer allows it. Indeed, if we consider the area S ₂ of the area of the second wall 134 forming the chamber, it is only on the resulting area S ₃ = Si-S ₂ of the first wall 132 that can be effectively exerted. the hydraulic pressure in the chamber to continue to slide the pusher 26. This pressure must therefore be increased to compensate for this difference if we want to continue the movement of the pusher in the direction of the spring. For example, if S _I / S ₃ = 4, it takes four times the pressure to continue moving.

Consequently, except to increase the pressure to the level necessary to continue the movement, the pusher 26 no longer moves once in contact with the second wall 134.

In figure 5, this is the phase between the pressure values C and D.

Thus the stressing of the stopper 30 of the washer 22 by the latter and of the washer 22 by the pusher 26 remains at a new level.

The stress on the second wall 134 by the pusher 26 appears and increases.

The curve “132 and 26” shows that the movement of the first wall 132 and of the pusher 26 relative to the housing is interrupted between point C and point D. And the second wall 134 remains stationary.

Before point C, the stop ring 28 receives the increasing forces due to the hydraulic pressure. After point C, that is to say once the pusher 26 is in abutment against the second wall 134, the stop ring 28 is not subjected to the additional stress resulting from the continued growth of the liquid pressure. The risks of the ring breaking are therefore reduced and there is no need to oversize this spring stopper. On the contrary, we can see on the part in dotted lines of curve 30/22; 22/26 that, without this limiting effect obtained with the invention, the increase in stress continues after point C.

The stop 138 of the pusher prevents any contact of the first wall 132 with the spring and limits after point C any stress associated with the hydraulic pressure on the spring and its stop ring so that it is not all of it. of the force due to the pressure reaching the spring and its stop ring.

In addition, the forces exerted by the first wall 132 on the pusher 26 are taken up at the level of the stop 138 by a large diameter, and therefore easily, the stop being located near an outer circumferential edge of the first wall.

After point D, with reference to FIG. 5, the first wall 132 and the pusher 26 move again. And for the first time, the second wall 134 begins to move. The stressing of the stopper 30 of the washer 22 by the latter and of the washer 22 by the pusher 26 resumes its growth. Nevertheless, beyond point D, the evolution of this stress as a function of the increase in pressure in the brake release chamber is reduced (the directing coefficient of the line representing the forces received by the part 30 as a function of the pressure beyond point D is smaller than when the pressure increased between A and B). And the solicitation of the second wall 134 by the pusher 26 continues to grow.

The invention thus makes it possible to provide if necessary high control pressures for the brake, since the stop ring of the washer is protected.

Provision can be made, in a non-illustrated variant of the machine, for the second wall 134 to be rigidly fixed to the casing 4. It may for example be in one piece with the latter or else constitute a separate part. In the latter case, it can be fixed to the housing in a sealed manner, for example by screws supplemented by gaskets.

The other characteristics of the machine are unchanged. FIG. 6 illustrates on this subject the same curves as in FIG. 5. These curves are identical up to point D. But the latter is no longer a characteristic pressure value knowing that the second wall 134 cannot move away from the point. housing as in the first case. The trend of the curves observed from point C therefore continues uninterrupted: the levels of curves 30/22; 22/26 and 132 and 26 persist after D. The curve 134/26 continues to increase. The level of the curve 30/22; 22/26 shows that the stop ring 30 of the washer remains protected against the increase in hydraulic pressure, in this variant.

Second embodiment

A second embodiment of the brake 212 of the machine has been illustrated in Figures 7 to 9 in three respective stages of operation.

In the description of this mode, as well as in that of the third which will follow, the characteristics of the machine which are not described again are assumed to be unchanged from those of the first mode. Furthermore, the reference numbers of certain elements are increased by 100. The stack of disks has not been shown. The same goes for the seals.

This time, the first wall 232 is rigidly fixed to the pusher 26, and is even in this case in one piece with the latter. The wall extends perpendicularly to the axis XX from the internal face of the pusher directed towards the axis, at a distance in the axial direction from the axial end of the pusher coming into contact with the spring 22, illustrated on the left on Figures 7 to 9.

The operation is similar to that of the previous embodiment.

FIG. 7 illustrates the brake 212 at rest, in a braking situation. The spring 22 biases the pusher 238 in the axial direction against the stack of discs. The second wall 234 bears axially against the shoulder 40. The stop ring 28 prevents axial displacement, in the direction opposite to the discs, of the internal edge of the spring 22. It is essentially subjected to the axial loading of the spring. If hydraulic pressure is applied in the chamber 24 delimited by the walls 232 and 234, the pusher 26 and the shaft 4, no displacement occurs as long as the force resulting from the pressure exerted on the first wall 232 does not exceed the force exerted in the opposite direction by the spring on the pusher.

If the hydraulic pressure makes it possible to overcome the force of the spring, the assembly consisting of the pusher 26 and the first wall 232 moves integrally in the direction of the spring, against the latter, to move away from the spring. discs. We are therefore in a situation of brake release. The second wall 234 remains stationary and in contact with the shoulder 40 of the shaft. This movement continues until the shoulder 42 of the pusher comes into contact with the second wall 234. This situation is illustrated in FIG. 8.

Referring to Figure 9, if the sliding of the pusher continues, it takes place by taking with it the second wall 234 at the level of the shoulder 42. If it is therefore desired to continue sliding the pusher, it is necessary as previously increase the hydraulic pressure accordingly to compensate for the reduction in the area of the first wall 232 on which the hydraulic pressure can be effectively exerted in order to continue movement. We are then in the situation of FIG. 9, with a space 50 which appears in the axial direction between the second wall 234 and the shaft 4. If this increase in pressure does not take place, the movement therefore does not occur. not beyond the situation shown in figure 8.

In this embodiment, it is the pusher itself which forms the stop 238 which prevents the first wall 232 from coming to bear against the spring 22.

Third embodiment

In a third embodiment which can also be represented by FIGS. 7 and 8, the brake differs from the second mode only in that the second wall is rigidly fixed to the housing. It can for example be in one piece with the latter or well constitute a separate room. In the latter case, it can be fixed to the housing in a sealed manner, for example by screws supplemented by gaskets. These screws are not shown.

During the operation of the brake, the movement of the pusher in the direction of the spring is therefore limited in its travel by its bringing into contact with the second wall. The latter thus defines this time the end of stroke of the pusher during brake release.

From a certain pressure corresponding to the crushing of the spring when the pusher is in the stop position, the brake is completely released, and even if the pressure still rises, no additional force will be transferred to the parts 22, 28 and 30.

Of course, numerous modifications can be made to the invention without departing from the scope thereof.

In particular, the invention is applicable to a large number of configurations of hydraulic machines. It is also possible to a very large extent to modify the shape of the housing, of the shaft, of the pusher, and of the first and second walls, as well as the relative arrangement of all these elements.

The machine according to the invention can be used as a motor or as a pump on different types of machinery or vehicles. It may for example be a wheel hub motor.

Claims

1. Hydraulic piston machine (2), comprising:

- a box (4),

- a tree (6),

- a cam (14),

- a block (8) with cylinders (16) and pistons (18) able to cooperate with the cam, and

- a brake (112; 212), the brake comprising:

- a stack of discs (20) connected alternately to the housing and to the shaft,

- a spring (22),

- a pusher (26) biased by the spring to put the discs in mutual support, and

- a first wall (132; 232) and a second wall (134; 234) interposed between the spring and the discs with reference to an axial direction (XX) of the shaft and delimiting a chamber (24) with the pusher so that when a liquid pressure in the chamber exceeds a predetermined threshold, the pusher moves against the spring, the first wall (132; 232) being interposed between the spring and the second wall with reference to the axial direction and mounted movably relative to the housing, the machine comprising a stop (138; 238) limiting a stroke of the first wall (132; 232) in the direction of the spring so that the first wall remains distant from the spring, the machine being arranged so as to so that the pusher (26) bears axially against the second wall (134; 234) when the pusher moves against the spring.

2. Machine according to the preceding claim, arranged so that the pusher (26) bears against the second wall (134; 234) by a shoulder (42).

3. Machine according to at least any one of the preceding claims, in which the stop (138; 238) is carried directly by the pusher.

4. Machine according to at least one of the preceding claims wherein the stop (138; 238) extends closer to a peripheral edge of the first wall (132; 232) than to an internal edge of the first. wall.

5. Machine according to at least any one of the preceding claims wherein the first wall (132) is mounted movably relative to the pusher.

6. Machine according to at least any one of claims 1 to 3 wherein the first wall (232) is rigidly fixed to the pusher.

7. Machine according to the preceding claim wherein the first wall (232) is in one piece with the pusher.

8. Machine according to at least any one of the preceding claims wherein the second wall (134) is movably mounted relative to the housing (4).

9. Machine according to at least any one of claims 1 to 5 wherein the second wall (234) is rigidly fixed to the housing (4).

10. Vehicle or machine, comprising at least one machine (2) according to at least any one of the preceding claims.