FR3149657A1 - Rotating hydraulic machine equipped with braking devices - Google Patents

Abstract

The rotating hydraulic machine (100) comprises: - a housing (2), - a shaft (20) mounted so as to be rotatable relative to the housing, - brake discs (25) configured to immobilize the shaft in rotation relative to the housing, - a static brake piston (30) configured to generate a compression of the discs (25) under the effect of a return member (32), and - a dynamic brake piston (40) configured to generate a compression of the discs under the effect of a fluid pressure, the machine being configured such that the static brake piston (30) generates the compression of the discs independently of the dynamic brake piston (40). Abstract figure: Fig. 2

Description

Rotating hydraulic machine equipped with braking devices FIELD OF THE INVENTION

The invention relates to rotating hydraulic machines and their braking members.

STATE OF THE ART

Document FR-3 048 042 discloses a rotating hydraulic machine equipped with a brake comprising disks configured to immobilize the shaft in rotation relative to the housing. A static brake piston is used to compress the disks against each other under the effect of a return member. An application of fluid pressure is used to compensate for the return force and to allow the shaft to rotate. This is a parking brake, negative brake or even an emergency brake.

We also know of hydraulic machines equipped with a dynamic brake piston ensuring the compression of the discs under the effect of fluid pressure. This is a service brake or positive brake.

An object of the invention is to provide a machine equipped with braking means whose arrangement is more efficient.

For this purpose, a rotating hydraulic machine is provided comprising:

- a crankcase,

- a shaft mounted mobile in rotation relative to the casing,

- brake discs configured to immobilize the shaft in rotation relative to the housing,

- a static brake piston configured to generate compression of the discs under the effect of a return member, and

- a dynamic brake piston configured to generate compression of the discs under the effect of fluid pressure,

the machine being configured so that the static brake piston generates the compression of the discs independently of the dynamic brake piston.

The machine may also have at least one of the following characteristics:

. it is configured so that the dynamic brake piston generates the compression of the discs independently of the static brake piston.

. it includes a support member configured to:

- be in abutment against the static brake piston without being in axial abutment against the dynamic brake piston by reference to an axial direction of the machine, and

- be in support against the dynamic brake piston without being in axial support against the static brake piston.

. the support member or the dynamic brake piston passes through an orifice of the static brake piston by extending from two sides of the static brake piston opposite each other in the axial direction.

. the machine is configured such that a ratio of a thrust produced by the support member against the dynamic brake piston under the effect of a fluid coming from a brake release chamber to a thrust produced by the dynamic brake piston against the support member by the fluid pressure is less than 15%, preferably less than 10%, and for example less than 5%.

. the support member or dynamic brake piston has a “T” shape.

. the static brake piston is interposed between the dynamic brake piston and the discs.

. the dynamic brake piston is slidably mounted in an end piece of the housing.

. the static brake piston is slidably mounted in the end piece of the housing.

. the machine includes a valve configured to discharge fluid flowing through the discs and coming from a braking chamber delimited by the static brake piston, the valve being configured not to discharge the fluid when the static brake piston causes compression of the discs.

. the valve is mounted in the shaft and the shaft has a radial conduit connecting the brake chamber with the valve.

. the machine includes a flow restriction downstream of the valve.

The invention also provides a vehicle or machine comprising at least one machine according to the invention.

It can be expected that the vehicle or machine includes:

- a brake control member configured to control an application of fluid pressure to the dynamic brake piston and/or

- a brake control member configured to interrupt an application of fluid pressure to the static brake piston.

The vehicle or machine may be provided to include a hydraulic pump configured to produce fluid pressure.

Finally, according to the invention, there is provided a method of braking a rotating hydraulic machine, in which method:

- a dynamic brake piston generates a compression of brake discs in order to immobilize a shaft of the machine in rotation relative to a casing of the machine under the effect of fluid pressure, and

- a static brake piston causes compression of the discs under the effect of a return organ and independently of the static brake piston.

DESCRIPTION OF FIGURES

We will now present embodiments of the invention as non-limiting examples in support of the drawings in which:

- there is an axial sectional view of a rotating hydraulic machine,

- there is a similar view showing a part of a machine according to a first embodiment of the invention;

- figures 3 to 5 are examples of equipment comprising such a machine;

- there is a view of a control circuit of a vehicle or machine comprising such a machine; and

- figures 7 and 8 illustrate two other embodiments of the machine of the invention.

Throughout the sequence, a bar is worth 10 ⁵ Pa.

First embodiment

We will present a first embodiment of the invention with reference to figures 1 and 2. The machine 100 according to this first embodiment is for example of the type illustrated in .

General layout

In all that follows, unless otherwise indicated, the parts are coaxial, symmetrical in revolution and centered on the X axis of rotation of the machine, which therefore defines its axial direction.

This is a rotating hydraulic motor that comprises a shaft 20 to which the hub of a wheel R can be secured, and a brake system configured to block the rotation of the shaft on command or when the brake system is not powered. Thus, by default, the shaft 20 is immobilized. It extends along the longitudinal axis X and rotates around this axis. It is driven in rotation by splines (not shown in the figures).

The engine comprises a crankcase 2 comprising a bearing cover 3 and a timing cover 4. It comprises a cylinder block 6 inside which are arranged radial pistons 8 mounted sliding inside their respective cylinders and equipped with a roller at one end. The engine comprises a lobed cam 10, rigidly fixed to the crankcase and on which the pistons 8 roll, thus performing a reciprocating movement inside their cylinders. The cylinders are supplied with pressurized oil (up to 450 bars) and rotationally secured to the cylinder block 6. The latter is rotationally secured to the shaft 20, either by a fixed connection or by a clutch. Splines, not shown, can form such a connection.

High pressure and low pressure supplies 16, 18 are located in the distribution cover 4, and more precisely in a distributor 12. The distribution cover 4 covers the distributor while being located radially to the outside.

On the other side of the cylinder block 6, the bearing cover 3 protects bearings 14, 15 which allow the rotation of the shaft while acting as a transmission of the force to the engine casing, the casing being secured to the chassis of the vehicle. Several types of engines exist with regard to the architecture of the bearings (resumption of force via the shaft or the hub of the wheel) and will not be detailed here. The shaft 20 is for example connected to the wheel R by means of a hub/stub axle located at the external end 24 of the shaft 20 and comprising holes for receiving screws securing the wheel. More generally, the external end 24 acts as an output for the drive shaft 20, and forms the recovery point of the torque produced by the engine.

The brake members can be positioned at the internal end 26 of the shaft. By internal, we mean the end opposite the external end 24. In the case of hydraulic torque assistance, this internal end is located furthest inside the vehicle.

It is also possible that the shaft 20 stops at the cylinder block 6 and is extended by a brake shaft 30, itself driven by the cylinder block, as illustrated in . The brake shaft 30 can therefore be separate from the drive shaft 20. The two shafts are connected by the splines of the cylinder block. The engagement of each shaft in the block can be unequal.

Braking organs

We will now describe the braking means of the first embodiment with reference to the . On the , these means have not been illustrated in detail. The machine 100 comprises:

- brake discs 25 configured to immobilize the shaft 20 in rotation relative to the casing 2,

- a static brake piston 30 configured to generate compression of the discs 25 under the effect of a return member 32, and

- a dynamic brake piston 40 configured to generate compression of the discs under the effect of fluid pressure.

The discs 25 form two series of discs, namely a first series of discs 25 integral in rotation with the shaft 20 and a second series of discs 25 integral in rotation with the housing 2. The discs of the first series are intercalated between those of the second. All the discs form a single stack in a direction parallel to the axial direction. When one of the brake pistons 30, 40 approaches the discs 25, it causes them to clamp as will be seen, thus causing the immobilization of the shaft 20 relative to the housing by friction of the discs. The discs 25 typically comprise a replaceable brake lining. Another possibility is to provide that the brake discs are made of nitrided steel.

The machine 100 comprises a brake cover 5 forming part of the casing 2, and therefore integral in particular here with the distribution cover 4. The brake cover 5, substantially of revolution, defines a volume V inside which the brake pistons 30, 40 are housed. A plate or cover 7 longitudinally closes an end opening of the cover 5. It rests on the cover 5 and closes the volume V.

Seals are provided to prevent oil leaks under pressure. A static seal is a seal that undergoes small movements, mainly in translation, and a dynamic seal is a seal that undergoes a rotational movement at the speed of the motor shaft. Static seals are more likely to be O-rings or quadrilobes, while dynamic seals are lip seals or composite seals comprising a sliding ring and a counter-seal for support.

The dynamic brake piston

The dynamic brake piston 40 has in this case a disk shape of axis XX. It is mounted in a blind cylindrical housing 44 of the plate 7, open towards the internal volume V of the machine. It is free to rotate relative to the casing around the axis XX and especially to slide relative to the plate 7 in the axial direction. A static seal 46 ensures the seal between the periphery of the piston 40 and the internal face of the housing 44. The seal 46 is received for example in an annular housing of the piston 40.

The static brake piston

In volume V is received the static brake piston 30. It has the general shape of a disk with axis XX and more precisely of a crown having a central through hole 33. It is also mounted sliding in the axial direction XX relative to the cover 5 with the interposition of a static seal 34 between the periphery of the piston 30 and the cover. The seal 34 is received for example in an annular housing of the cover 5. The static brake piston 30 has an excess thickness in the central part on its face directed towards the dynamic brake piston 40, and an excess thickness in the peripheral part on its face directed in the opposite direction.

An oil inlet pipe 36 supplies a brake release chamber 38 delimited between the static brake piston 30 and the brake cover 5 in the volume V and configured so that the pressurized oil pushes this piston in the direction of the plate 7, that is to say in the direction opposite the discs 25.

On the other side of the piston 30, the return member 32 generates a counterforce which tends to maintain this piston in the braking position, that is to say with the discs 25 pinched. When the brake system is not supplied with pressurized oil, this member immobilizes the shaft 20 via the piston 30 and the discs. It takes the form of a washer or springs, for example. It is housed in a cavity or chamber 39 called dry of the volume V , as opposed to the brake release chamber 38 which receives pressurized oil. The dry chamber 39 and the brake release chamber 38 do not allow fluid to be exchanged between them. They are formed by the division of the volume V by the static brake piston 30 into two sub-volumes. Consequently, they are located longitudinally on either side of this piston.

The support organ

The machine further comprises a support member 50 having in this case a “T” shape. This member comprises in this example a flange 52 having a general shape of a disk of axis XX having on one face a rim 53 extending opposite the disks 25, and on the opposite face a central slide 54 of diameter D much smaller than that of the flange 52 and forming on this face a projecting relief. This slide extends into the orifice of the static brake piston 30. The support member 50 thus passes through the orifice of the static brake piston 30 by extending on two sides of this piston opposite one another in the axial direction XX.

With this arrangement, the static brake piston 30 is interposed between the dynamic brake piston 40 on the one hand and the flange 52 and the discs 25 on the other hand. Similarly, the flange 52 is interposed between the two pistons 30, 40 on the one hand and the discs 25 on the other hand.

The static brake piston 30 here has a crown shape. It is surrounded by the brake cover 5 and surrounds the support member 50. It is guided by the cover 5.

We therefore see that the support member 50 is configured to:

- be in abutment against the static brake piston 30 without being in axial abutment against the dynamic brake piston 40 and

- be in support against the dynamic brake piston 40 without being in axial support against the static brake piston 30.

To isolate the brake release chamber 38, static seals are provided:

- between the brake cover 5 and the static brake piston 30, and

- between cover 5 and distribution cover 4,

and dynamic seals 14 are provided between the shaft and the distribution cover 4 since these seals receive a rotational movement when the engine is running. Thus, between the brake cover 5 and the distributor 12, to avoid oil leaks since the discs are immersed in oil, an annular seal 60 is provided radially around the shaft 20.

The support member 50 is centered by the piston 30 at the level of the slide 54. It is also at this level that the seal between the two parts is provided by a static seal 62 arranged in a groove made in the piston 30.

Braking actions

As indicated above, by default, the static brake piston 30 is in the braking position when no pressurized oil is injected into the brake release chamber 38. The washer 32 therefore pushes this piston 30 against the flange 52 of the support member 50, pushing the latter into abutment against the discs 25 to cause them to tighten. This is therefore static or parking braking which can also be used as an emergency brake. As soon as pressurized oil is injected into the brake release chamber 38, the static brake piston 30 undergoes a translation away from the discs, and allows the shaft 20 to rotate. This piston 30 operates as a “negative brake”. It is observed that it generates the compression of the discs independently of the dynamic brake piston 40. The parking brake is a negative brake that is applied in the absence of a command, which makes the machine safe when it is stopped, for example typically in the case of a wheel or cylinder drive motor. When the machine stops or in the event of a hydraulic failure, this brake is applied automatically. It is observed that the static brake piston 30 generates the compression of the discs independently of the dynamic brake piston 40.

A conduit 42 is provided to supply fluid to a braking chamber 43 delimited at the bottom of the housing 44 of the dynamic brake piston 40. This conduit extends here into the plate 7. When a fluid pressure is applied to this chamber 43 and provided that the static brake piston 30 is in the braking position, the dynamic brake piston 40 is moved in the direction of the discs 25, to the right on the . It comes into direct support against the slide 54 of the support member 50 and therefore requests the latter to tighten the discs. We therefore obtain a service brake function or dynamic brake used when driving the machine. We observe that the dynamic brake piston 40 generates the compression of the discs independently of the static brake piston 30.

We are therefore in the presence of a combined brake system which performs the two functions by acting on the same pack of brake discs and in this case via the same support member 50. This machine therefore implements a braking process in which:

- the dynamic brake piston 40 generates a compression of the discs 25 in order to immobilize the shaft 20 in rotation relative to the casing 2 under the effect of fluid pressure, and

- the static brake piston 30 generates a compression of the discs under the effect of the return member 32 and independently of the dynamic brake piston 40.

Offset ratio

The energy efficiency of dynamic braking is particularly interesting here. To see this, we consider:

- the thrust produced by the support member 50 against the dynamic brake piston 40 under the effect of the fluid coming from the braking chamber 38, towards the left on the , And

- the thrust produced by this piston 40 against the support member 50 by the fluid pressure exerted from the control conduit 42 of this piston, towards the right on the .

The ratio of the first push to the second is here less than 15%, and even 10% and 5% as we will see.

Such a ratio, called an offset ratio, can be defined in pressure or in diameter.

Dynamic braking can only occur in the brake release position of the static brake piston 30. The brake release pressure is exerted in the brake release chamber 38, on the face of the static brake piston 30 facing the discs, and for what interests us here, on the two faces of the support member 50 located in this chamber. This is its entire face facing the discs and its opposite face, with the exception of the slide 54. It is therefore the presence of the latter which generates a difference in thrust on the two faces of the support member 50, thus producing a net thrust of this member in the direction of the dynamic brake piston 40, to the left. In this case, the net thrust corresponds to the surface area of the section of the slide 54 in a plane perpendicular to the axis XX. (This surface area is π.D ² /4).

The pressure offset ratio is also dependent on the dynamic braking pressure. For the latter, for example, when a brake is said to be "at 120 bar" in the specifications or in the catalog, it is in fact used at 72 bar most of the time for normal braking. In this case, we define the pressure offset ratio for 120 bar as an example. It is therefore a question of comparing the thrust of the braking pressure (for example constant at 30 bar) transmitted by the slide 54 to the thrust of the dynamic brake piston 40 (typically at 72 bar, but 120 bar is also taken into account for maximum braking) which is exerted on the entire section of the dynamic brake piston 40.

The geometric ratio is the ratio of the diameter of the slide 54 to that of the dynamic brake piston 40 which defines the operation for a nominal pressure of 30 bar on one side, and 120 bar (or 72 bar) on the other. In this first embodiment, the diameter of the slide is 11.8 mm. In the second embodiment which will be described later in relation to the , this diameter is 40 mm. The “Other case” line corresponds to a slide diameter of 24 mm. The offset ratio values are in Table 1 below.

Diameter D of the slide Piston diameter 40 Diameter ratio Offset ration at 72 bar Offset ratio at 120 bar First mode 11.8 mm 40 mm 0.295 4% 2% Second mode 20 mm 40 mm 0.500 10% 6% Other case 24 mm 40 mm 0.6 15% 9%

The lower the offset ratio, the less the dynamic brake piston 40 must provide for braking, i.e. the less it must compensate for the static brake release pressure. This ratio decreases when the reference dynamic brake pressure is increased. A particularly low offset ratio is therefore observed when activating the dynamic brake since the pressure in the brake release chamber 38 only generates a force to be overcome over a very small section corresponding to that of the slide 54.

The valve

The machine also comprises in this case a valve 70 mounted in the shaft 20, in particular in a housing 72 opening at one end of the shaft oriented towards the brake cover 5. The shaft has a radial conduit 74 putting a chamber 75, located on one side of the disks 25 opposite the support member 50, in communication with the valve 70. The shaft 20 also has an axial conduit 76 putting the housing 72 and therefore the valve in communication with a zone of the shaft remote from the latter. With reference to a direction of a flow of fluid in the valve as we will see, the radial conduit 74 is upstream of the valve and the axial conduit 76 downstream. A flow restriction 78 is provided in the axial conduit downstream of the valve 70.

The valve can be represented as a calibrated flap. It aims to prevent the circulation of fluid below a first predetermined threshold, for example 15 bar, to allow a pressure increase in the brake release chamber 38 when the brake release is hydraulically activated by exerting pressure through the conduit 36 (emergency brake release). It is therefore configured not to evacuate the fluid when the static brake piston 30 causes the compression of the discs.

Beyond a second, preliminary threshold, for example 13 bars, we know that there is enough pressure in the chamber 38 to counteract the force of the washer 32 and release the static brake piston 30. The valve is therefore configured to evacuate fluid flowing through the discs and coming from the brake release chamber 38. Beyond the first threshold, a circulation of fluid therefore takes place through the valve 70 to perform an oil flush in order to renew the oil and cool this part. This also makes it possible to evacuate dust, or even particles resulting from the wear of the brake discs. This flushing is done from the brake release chamber 38. A flow therefore passes through the latter, passes between the support member 50 and the cover 5, passes through and cools the disks 25 and opens into the radial conduit 74 which arrives at the valve 70. Then the rinsing-cooling flow leaves the valve via the axial conduit 76 through the shaft 20 and the restriction 78, towards the casing of the machine, then is drained by a brake pipe which returns the fluid to a pressureless oil reservoir. Incidentally, the flushing circuit can collect leaks from the dynamic seal 74.

But this circulation is limited by the restriction 78 which makes it possible to maintain a pressure difference despite the circulation of fluid and therefore to maintain a pressure in the brake release chamber 38 so that the static brake is not activated. In this way, the force exerted by the washer 32 on the static brake piston 30 is constantly countered so that the stack of discs is not compressed by the support member 50. In other words, the valve 70 has the function of maintaining the minimum pressure, for example 13 bars, in the brake release chamber 38, while the restriction 13 has the function of limiting the flow rate so as not to exhaust the hydrodynamic braking system. This is especially valid in emergency mode, because in normal operating mode this valve could be dispensed with.

It is indeed noted that such a configuration forms a hydrodynamic braking system, because it is based on a pressure balance that is created and maintained by a flow rate. In other words, during braking, this hydrodynamic braking system delivers a flow rate permanently. Such a system is supplied by a flow of pressurized hydraulic fluid, for example by means of a three-way proportional valve, and a source of dynamic pressure such as a pump drawing from a reservoir of hydraulic fluid, and has a line connected to a reservoir of unpressurized fluid. A description of such a system can be found in publications FR-3 054 513 in support of figures 6a and 6b and FR-3 052 723 in support of figures and 7.

Vehicle or machine

A vehicle or machine may be provided comprising one or more such machines, for example as a motor for travel wheels. This machine is particularly suitable for a sweeper 80, a tool carrier 81 or a forklift 82 respectively illustrated in FIGS. 3, 4 and 5, or a compactor or a road roller. In the following, when we speak of a vehicle, it is understood that this will also apply to a machine.

The control circuit 101 of such a vehicle is illustrated in . In this vehicle, each drive wheel 83 is equipped with a motor 100 forming a machine according to the invention. In the figure, a front wheel 83 and a rear wheel 83 thus equipped are illustrated.

The circuit 101 comprises a hydraulic fluid reservoir 84 and a pump 85 supplied by the reservoir. It comprises a pressurization pump 86 for the part of the circuit providing service braking. It supplies the two motors 100 with the interposition of a brake control member 87 configured to generate via a valve of the member and a brake line connected to the conduit 42 an application of fluid pressure to the dynamic brake piston 40 of each motor. This member is used during driving and ensures loading of the valve. It is for example a pedal which provides an output flow at a modulated pressure. The more the pedal is pressed, the more intense the dynamic braking. When the pedal is released, the valve relieves the pressure of the brake line up to the pressure of the reservoir 84. The valve associated with the pedal 87 is shown below the pedal.

The circuit 101 also includes a pump 88 for pressurizing the part of the circuit providing parking braking. In this case, it supplies only one of the two motors 100, for example that of the rear wheel with the interposition of a braking control member 89, such as a lever, configured to interrupt an application of fluid pressure on the static brake piston 30 when the lever is actuated. This member serves as a static braking control for parking. It has reverse control and includes a similar valve but which interrupts the fluid pressure when the member is actuated, for example when the lever is lowered. The valve is also proportional to three ways, and provides a line with a braking flow, that is to say a flow at a modulated pressure, from a pressure line coming from the pump and a pressureless line connected to the reservoir 84.

Electrical controls can replace these manual controls, in the case of a machine controlled by an automation system.

Such a machine does not require the use of a separate specific parking brake, for example in the form of a drum brake which is a more expensive and less reliable solution.

Second embodiment

We will present a second embodiment of the machine of the invention with reference to the . Features identical to those of the first mode will not be described again.

On the machine 200, it is found that the static brake piston 30 extends in the axial direction opposite the periphery of the face of the support member 50 opposite the disks 25 and that the dynamic brake piston 40 is located opposite the central slide 54 of the support member. This time, however, the slide 54 is mounted movably by sliding in the housing 44 of the plate 7 receiving the dynamic brake piston 40 with the interposition of a static seal 290, here housed in a groove of the plate. In addition, the static brake piston 30 is mounted to slide in the plate 7, with the interposition of the static seal 34, here housed in a groove of the plate 7. The plate 7 comprises a central cylindrical sleeve 292 defining in the internal part the housing 44 of the dynamic brake piston 40 and the slide 54. It forms in the internal part the guide support of the dynamic brake piston 40 and the slide and in the external part that of the static brake piston 30 with the interposition of a static seal 294, in this case carried by the sleeve 292. The arrival of the control fluid of the dynamic brake piston 40 can for example be done this time via an axial orifice 242 passing through the plate 7 along the axis X-X. The operation of the two brakes is unchanged. The valve 70 is absent here. A static seal 293 ensures the seal between the support member 50 and the shaft, at the level of the slide 54 which this time also extends in the direction of the shaft, in the latter.

Third embodiment

We will present a third embodiment of the invention with reference to the . Features identical to those of the first mode will not be described again.

This time, in the machine 300, the shape of the dynamic brake piston 40 and the support member 50 are reversed in comparison with the first mode. Thus, it is this piston which has a “T” shape and comprises a central slide 54 projecting from the face of the disk oriented towards the support member 50. This slide passes through the central orifice of the static brake piston 30 to be able to come into contact with the support member located on the other side of this piston. The support member 50 is devoid of a slide and has a general disk shape although its central part is slightly bulged in this case for reasons of space.

The operation remains unchanged.

Many modifications can be made to the invention without departing from its scope. The machine according to the invention could also function as a pump.

Claims (16)

Rotating hydraulic machine (100; 200; 300) comprising:
- a casing (2),
- a shaft (20) mounted to rotate relative to the casing,
- brake discs (25) configured to immobilize the shaft in rotation relative to the housing,
- a static brake piston (30) configured to generate compression of the discs (25) under the effect of a return member (32), and
- a dynamic brake piston (40) configured to generate compression of the discs under the effect of fluid pressure,
the machine being configured so that the static brake piston (30) generates the compression of the discs independently of the dynamic brake piston (40). Machine according to the preceding claim, configured so that the dynamic brake piston (40) generates the compression of the discs (25) independently of the static brake piston (30). Machine according to one of the preceding claims which comprises a support member (50) configured to:
- be in abutment against the static brake piston (30) without being in axial abutment against the dynamic brake piston (40) with reference to an axial direction (X) of the machine, and
- be in support against the dynamic brake piston (40) without being in axial support against the static brake piston (30). Machine according to the preceding claim in which the support member (50) or the dynamic brake piston (40) passes through an orifice (33) of the static brake piston (30) extending on two sides of the static brake piston (30) opposite each other in the axial direction (X). Machine according to one of claims 3 or 4 configured so that a ratio:
- a thrust produced by the support member (50) against the dynamic brake piston (40) under the effect of a fluid coming from a braking chamber (38)
- on a thrust produced by the dynamic brake piston (40) against the support member (50) by the fluid pressure
is less than 15%, preferably less than 10%, and for example less than 5%. Machine according to one of the preceding claims in which the support member (50) or the dynamic brake piston (40) has a “T” shape. Machine according to one of the preceding claims in which the static brake piston (30) is interposed between the dynamic brake piston (40) and the discs (25). Machine according to one of the preceding claims in which the dynamic brake piston (40) is slidably mounted in an end piece (7) of the casing. Machine according to the preceding claim in which the static brake piston (30) is slidably mounted in the end piece () of the casing. Machine according to one of the preceding claims which comprises a valve (70) configured to evacuate fluid flowing through the discs (25) and coming from a braking chamber (38) delimited by the static brake piston (30), the valve being configured not to evacuate the fluid when the static brake piston causes compression of the discs. Machine according to the preceding claim in which the valve is mounted in the shaft and the shaft has a radial conduit (74) connecting the brake release chamber (38) with the valve (70). Machine according to one of claims 10 or 11 which comprises a flow restriction (78) downstream of the valve (70). Vehicle (80; 81; 82) or machine comprising at least one machine according to any one of the preceding claims. Vehicle or machine according to the preceding claim which comprises:
- a brake control member (87) configured to control an application of fluid pressure to the dynamic brake piston (40) and/or
- a brake control member (89) configured to interrupt an application of fluid pressure to the static brake piston (30). A vehicle or machine according to claim 13 or 14 which comprises a hydraulic pump (86) configured to produce fluid pressure. Method of braking a rotating hydraulic machine (100; 200; 300), in which method:
- a dynamic brake piston (40) generates a compression of brake discs (25) in order to immobilize in rotation a shaft (20) of the machine relative to a casing (2) of the machine under the effect of a fluid pressure, and
- a static brake piston (30) generates the compression of the discs under the effect of a return member (32) and independently of the static brake piston.