EP1241352B1 - Hydraulic motor or pump with means for rotationally connecting two housing parts - Google Patents

Description

The present invention relates to a hydraulic device such a motor or a pump comprising a first part made up by a part of the casing in which is disposed a cylinder block and a second part fixed to this first part, the device comprising a system for securing the two parts in rotation so as to allow the passage of a couple between these parts, the latter each having a contact face, the two contact faces being held together by means of coercion axial, said system comprising at least two sets of secured in rotation each comprising two aligned holes, respectively practiced in each of the two rooms and opening in their respective contact faces, as well as a shear extending in these holes, the shear members being able to withstand the shear forces generated by the torque transmitted.

For hydraulic motors or pumps, the housing generally comprises several parts, which are machined individually, and which are assembled together. This assembly must allow the passage of a couple. For example, the casing of a hydraulic motor has a cam portion whose inner periphery is corrugated to cooperate with the pistons of the cylinder block and a so-called cover part distribution, arranged around the internal distributor that distributes the fluid to the cylinders of the cylinder block. These two parts must be fixed between them so as to be perfectly integral in rotation. In the case of a fixed casing, it is generally the cover part of distribution which is fixed to a fixed part such as the chassis of a vehicle, and the cam part must be perfectly fixed to this cover part without being able to turn, since it is the rotation of the cylinder block by compared to the cam which conditions the operation of the engine. In this case, the torque that is transmitted between the distribution cover and the Cam part is the torque resistant to the motor torque.

In addition, some hydraulic motors are fitted with braking systems which are arranged in a so-called housing part brake cover. This part is fixed to another part of the casing, by example the distribution cover and it should be perfectly integral in rotation to transmit the braking torque.

In the case of a crankcase motor, the engine torque or the braking torque must also be transmitted between the parts of crankcase assemblies.

It is known to assemble the different housing parts of a hydraulic motor by screws. These screws allow you to press one against the other the contact faces of the assembled housing parts. So a part of the torque to be transmitted between these parts is by forces friction between the two contact faces.

Overall, the friction forces are proportional to the axial support stresses of the contact faces against each other. For many applications, trying to transmit torque between parts fixed together by friction forces alone would require extremely high axial support stresses which would make it mandatory to design the screws accordingly fixing of the parts and of these parts themselves. this is not achievable in many applications, so that shear members which transmit torques higher while maintaining a limited space requirement of the device.

In known devices, e.g. US-A-3,844,198, these shear members are formed by cylindrical pins which are engaged in two cylindrical holes located opposite in the contact faces of the two pieces. These pawns and these holes must be sized to extremely precise because even a very small clearance between the pawns and the holes could allow a slight angular offset between the two pieces, cause relative movements between the two pieces, impair the transmission of torque and cause premature wear. When the motor or pump is reversible, i.e. its rotor can rotate relative to its stator in two opposite directions, the games and the relative movements between the two parts can even less be tolerated since the possible deformations linked to rotation in a sense, that is to say the passage of the couple in one direction, would cause games and relative movements that would interfere with the transmission of torque in the other direction of rotation. The risks of premature wear are even bigger.

It should also be noted that, in these systems, the positioning holes must be extremely precise so that both holes of each rotating fastening assembly are located exactly opposite.

As a result, the realization of the joining assemblies in rotation gives rise to extremely high manufacturing constraints demanding, with tight tolerances and extremely machining specific. This considerably increases the manufacturing costs.

In addition, disassembly of the parts is delicate and, in the event of wear cylindrical pins or holes, it is practically impossible reassembly without backlash. This would require a re-machining of the bores and the installation of pawns of dimensions more important.

For these reasons, we are led to limit as much as possible the number of fastening sets in rotation, accepting that a much of the torque is transmitted between parts by the forces of friction between their contact faces. In a given space, the number of screws and their size are limited. Similarly, the class of screws (normalizations) and the tightening torques applied to them are limits. In addition, the torque transmitted by friction is very dependent on the surface condition of the contact faces (coefficient of friction) and of the screw tightening torque (accuracy from ± 10% to ± 30%). Use adhesive on the contact faces has proven to be of limited effectiveness. This is not very secure for certain applications.

The object of the invention is to remedy the aforementioned drawbacks by proposing an improved system for securing in rotation between two parts of a hydraulic device such as a motor or pump between which a couple must be transmitted.

This goal is achieved thanks to the fact that for each set of secured in rotation, the shearing member and the bores have respective dimensions in the free state not allowing the contact between said contact faces when the shearing member is arranged in the holes, and the fact that for each set of secured in rotation, the shearing member cooperates without play with the holes and at least one of the elements constituted by the two holes and by the shearing member present, due to the application of said axial stress on the parts, a deformation in the field of homogeneous plastic deformations, said deformation affecting an area which is located in the vicinity but outside the plane of contact between the contact surfaces.

With the invention, unlike the prior art, it is not necessary to carry out machining adjusted to the dimensions of the members shear, but on the contrary we deliberately choose that these are too large for the holes. It is by assembling the parts that the holes and / or the shearing members are deformed to allow contact between the contact faces and the two parts. The axial stresses exerted on the parts during their assembly, by example by screws, must therefore be sufficient to overcome the stresses exerted by the shear members on the walls of the holes and which tend to separate these parts from each other, up to deform the holes and / or the shearing members. In doing so, we takes two essential precautions since it ensures, on the one hand, that the deformations carried out remain in the deformation domain plastic and homogeneous and, secondly, that they affect an area located outside the contact plane between the contact surfaces.

Homogeneous plastic deformations include a plastic deformation part and elastic part. By deformation plastic, there is a self-adjustment of the machining in relation to the ball and we ensures that the contact surfaces between the shearing members and the walls of the holes located opposite are sufficient for the stresses exerted between said holes and said members are correctly distributed. The elastic part of the deformations allows a disassembly and reassembly of parts without difficulty, and without risk of seeing a game to be established.

Once the parts are assembled and said deformations homogeneous plastics produced, the axial support constraints of the faces of contact against each other are partly used to overcome the tendency of parts to deviate from each other due to the part elastic deformation and, for the remaining part, to secure the two parts in rotation by friction. So the share of friction in the constraints of joining in rotation of the parts decreases, while that the part due to the reactions between the holes and the organs of shear increases compared to the prior art. Advantageously, the shear members transmit a torque on the order of 40% of the maximum torque to be transmitted, the remaining part being transmitted by the friction forces.

Knowing the mechanical characteristics of materials in which the borehole walls and the shear, in particular their hardness measured mainly by the Brinell method, the skilled person will be able to choose oversizing shear members with respect to the holes so that the deformations necessary to bring the contact faces are in the field of plastic deformations homogeneous.

Advantageously, the shearing members include marbles.

The balls have both the advantage of being simple and not very expensive to carry out, while being able to position themselves so optimal in the holes, due to their spherical shape.

Advantageously, the walls of the holes and the organs of shear are formed in materials which have hardnesses different. In this case, under the effect of axial tightening stresses of the two pieces against each other, or the walls of the holes, or well the shear members preferentially deform, so that we determine in advance which parties will be affected by the deformation.

In this case, advantageously, the walls of the holes are formed from a material that has a lower hardness than material in which the shear members are formed. Through example, we will choose to make the parts in which are formed these holes in a material such as steel or cast iron having a Brinell hardness for example between 100 and 250, while shear members, especially when it comes to steel balls for bearings, will have a Rockwell hardness between 58 and 65, or Brinell hardness greater than 600. Balls having a hardness of this order of magnitude, usually used for ball bearings, are produced in large economic series.

In this way, we make sure that the deformations only affect the holes. When using materials of different hardnesses, it is possible, by comparison with a Brinell test and using the data from standard EN 10003-1 on Brinell hardness, to determine a law relating the hardnesses of wall materials holes of each of the two parts at the contact diameters between the holes and the balls and at the respective depths (amplitudes) of the deformations and therefore at the positions of the contact zones between the holes and the balls with respect to the respective contact faces.
We observe : d2 d1 = HB1 / HB2 and h2 h1 = HB1 HB2 where d1 and d2 are the bore / ball contact diameters in the first and second parts, respectively;
HB1 and HB2 are the respective hardnesses of the first and second parts;
h1 and h2 are the depths (measured axially) of the deformations respectively produced in the first and second parts by the application of the contact faces against each other.

Advantageously, at least one of the holes of at least one assembly in rotation has a frustoconical part with which the shearing member cooperates.

The conical shape makes it possible to correctly wedge the shear against the wall of the hole, er. centering it in this hole.

In this case, preferably, at least one of the holes of at least at least one rotational securing assembly has a portion cylindrical and a frustoconical portion connected by a circular edge, said frustoconical portion being on the side of the contact face of the room in which the hole in question is formed; the organ of shear is in contact with this edge.

Thus, the contact zone between the shearing member and the wall of the hole is made on an edge. As a result, the material flows more easily under the effect of axial stresses which bring into contact the two contact faces of the two parts. Therefore, for a constraint given axial, one obtains a deformation of greater amplitude only if the contact zones between the shearing members and the drilling took place on tangential surfaces. When the organ of shear is harder than the material of the edge, the latter has tendency to deform when crushing. Otherwise, the edge has tendency to form a groove in the shearing member.

The edge located at the junction of the frustoconical parts and cylindrical, it forms an obtuse angle which allows, after the deformation, increase the contact surface between the shearing member and the wall of the hole, which favors the distribution of stresses shear.

In addition, this shape of the holes facilitates machining and deburring.

The contact surfaces between the holes and the shear are limited while remaining sufficient to ensure a torque transmission. For a given axial stress, the part of the constraint which is used to overcome the residual elasticity of the deformation of less contact edge and / or shear member than that which would be necessary if the contact surfaces were example of flat or cylindrical surfaces. As a result, we preserves a larger part of the axial stresses to be transformed into friction force between the contact faces.

In addition, the frustoconical portion of the hole is located towards the entry of this hole and allows to center the shearing member, so that it is positioned correctly on the circular edge. This centering function makes it possible to remedy any eccentricity faults between the facing holes and therefore allows less machining specific.

In addition, the frustoconical part prevents the deformation does not disturb the flatness of the contact face which is used for transfer of part of the couple by friction.

According to a particularly advantageous variant, one of the holes of at least one rotational securing assembly present a blocking section with which the shearing member cooperates in being stuck in the hole.

The shear member is forcibly engaged in the section of blocking of the drilling of the part considered, before the assembly of this piece with each other. The blocking section has dimensions transverse slightly lower than those of the shearing member, which allows the latter to be forcibly engaged manually, or using a tool such as a hammer. We can practice the same for shear members of each rotational securing assembly, which allows you to manipulate the part whose holes are provided with blocking sections with the shearing members arranged in these holes as a whole for the assembly of this piece with the other.

• la figure 1 est une vue en coupe axiale d'un moteur hydraulique équipé de systèmes de solidarisation en rotation conformes à l'invention ; et
• les figures 2 à 4 sont des vues de détail d'un ensemble de solidarisation en rotation, selon trois variantes.

The invention will be clearly understood and its advantages will appear better on reading the detailed description which follows, of an embodiment shown by way of nonlimiting example. The description refers to the attached drawings, in which:

• Figure 1 is an axial sectional view of a hydraulic motor equipped with rotational securing systems according to the invention; and
• Figures 2 to 4 are detail views of a rotational securing assembly, according to three variants.

The hydraulic motor in Figure 1 is a piston motor radial. It has a casing in four parts, 1A, 1B, 1C and 1D. The part 1B has a corrugated internal periphery and forms the cam against which react the pistons 2 'of the cylinder block 2. The engine shaft 3 is integral in rotation with the cylinder block by grooves and extends in part 1A of the casing, which carries the bearings 4 of the motor. This last includes an internal fluid distributor 5 whose conduits distribution 6 are alternately connected to the cylinder ducts 7 of the cylinder block 2. The distributor extends inside part 1C of the casing, called distribution cover. Inside the dispenser also extends a brake shaft 8 which, like the shaft 3, is integral in rotation of the cylinder block 2. The end of this shaft opposite to the cylinder block extends into part 1D of the housing, called the cover of brake. This end and this housing part carry braking constituted in this case by discs 9 interposed between others. A brake piston 10 is biased by a spring 11 to push the discs 9 into brake contact and can be controlled by reverse direction by supply of fluid to a brake chamber 12.

The motor shown in Figure 1 is of the shaft type rotating, since its housing is fixed, the housing part 1C comprising a flange 13 for fixing to an external element such as, for example, the chassis of a vehicle. Parts 1A, 1B and 1C of the housing are connected between them by fixing screws 14, while the parts 1C and 1D the are by fixing screws 15.

The engine torque is transmitted by the rotating cylinder block 2 to the shaft 3 which, by flanges 3 ', is intended to drive an element outside. To allow engine operation, it is important that the cam 1B is perfectly secured, with respect to the rotation about the axis A, of part 1C of the casing which is that which is fixed to a fixed element by the flanges 13. A torque resistant to the engine torque must therefore be transmitted between parts 1C and 1B of the casing. These present contact faces, respectively 1C 'and 1B', which are substantially planes and perpendicular to the axis of rotation A of the motor.

Similarly, when braking, the braking torque must be transmitted between the part 1D of the casing which carries those of the discs 9 which are fixed and part 1C. These parts 1D and 1C have faces of contact, respectively 1D "and 1C", which are also planar and perpendicular to axis A.

The screws 14 or 15 are used to exert axial stresses, between parts 1C and 1B respectively and between parts 1C and 1D, to press their respective contact faces against each other. Due to manufacturing tolerances and screw threads, the latter are not used for the transmission of the aforementioned couples.

These couples are transmitted by the friction forces between the contact faces which are generated due to the axial support between these faces and by rotational securing assemblies. So we see on Figure 1 a first set of rotational fastening 20 between the parts 1C and 1B, and a second set of rotational securing 30 between parts 1C and 1D. Although this is not visible on the section, the joining system between parts 1C and 1B comprises at minus two sets similar to set 20, while the system for fastening in rotation between the parts 1C and 1D comprises at least two sets similar to the set 30. One can for example provide three sets regularly spaced angularly but of course, this number can be higher.

The sets 20 and 30 are similar, and we describe more specifically the assembly 20. The latter comprises a bore 20B, which is practiced in part 1B of the casing and which opens in its face of contact 1B ', and a hole 20C, which is practiced in part 1C of casing and which opens in its contact face 1C '. The holes 20B and 20C are aligned on the axis A '. The set 20 also includes a shear member 22 which extends partly in each of the holes 20B and 20C. In the preferred example shown, this body shear consists of a ball.

We choose shear members capable of supporting the shear stresses generated by the transmitted torque. For example, we choose balls capable of supporting each of the constraints of shear of the order of 550 daN.

With reference to FIGS. 2A to 2C, we now describe the assembly 20 in more detail. Figure 2A partially shows these parts in their assembled position, in which a couple can be transmitted between them. We chose a ball 22 made of a harder material as that in which the walls of the holes 20B and 20C are produced, and we see that this ball is not or practically not deformed, while that said walls are slightly so. Thus, the ball cooperates without play with the walls of each of the two holes.

Figure 2B shows the same assembly before assembling the parts 1B and 1C, in a position in which the ball 22 touches simply the walls of the holes 20B and 20C without constraints are exerted to bring parts 1B and 1C closer to one of the other. In this position, we see that the contact faces 1B 'and 1C' are separated by a distance D1. To move from the situation of the figure 2B to that of FIG. 2A, it is necessary to exert axial stresses on the parts 1B and 1C, for example using screws 14 or using a device exterior such as a press, at least for bringing the faces 1B 'into contact and 1C 'and defeat the resistant efforts opposed to this rapprochement by the cooperation between the ball and the walls of the holes 20B and 20C. This doing so, the walls of the holes and / or the ball 22 are deformed, this remaining deformation in the field of plastic deformations homogeneous.

Preferably, the axial support constraints between the faces 1B 'and 1C' are even greater than the minimum constraints required to overcome the aforementioned resistant efforts, so that the constraints exceeding these minimum stresses are at the origin of forces of friction between these two faces.

In the embodiment shown, each of the holes 20B and 20C includes a frustoconical part, respectively 24B and 24C opening at its wide end in the contact face 1B ', respectively 1C 'and a cylindrical part, respectively 26B and 26C located on the side opposite to said contact face. For each drilling, these parts are connected by a circular edge, respectively 25B and 25C. In the example of FIGS. 2A to 2C, the two holes 20B and 20C are identical, that is to say that their respective cylindrical portions have the same diameter D, that the angle at the top of the frustoconical portions α is the same and that the distance H between the circular edge 25C or 25B and the face contact 1C 'or 1B' is the same. We advantageously choose that the angle α is between 70 ° and 110 °, preferably of the order of 90 °. Very advantageously, it is chosen that the axial distance H is included between 15% and 40% of the diameter D, preferably between 20% and 30% of this diameter. As we will see below with reference to Figure 3, the two holes can be different, but the above values for the angle α and the H / D ratio can remain within the same ranges, in being for example at the two extremes of these ranges.

Figure 2C shows the same set 20 after a disassembly, in a position in which parts 1C and 1B are only close together so that the ball touches the walls of the holes without exerting any particular constraints on them.

We see that the edges 25B and 25C have been deformed by compared to the situation in Figure 2B. The deformation visible in the figure 2C is the purely plastic and non-reversible part of the deformation which has been brought. However, even in the situation in Figure 2C, the contact faces 1B 'and 1C' of parts 1B and 1C are not in contact, but are separated by a distance D2. To replace these faces in contact one against the other and again allow the passage of a couple between parts 1B and 1C, it is necessary to further deform the edges 25B and 25C. This remaining part of the deformation is the residual elasticity which is reversible. Even after disassembly and reassembly, we can easily obtain clearance-free contact between the shearing member, by example ball 22, and the holes.

Preferably, we make sure that the elastic part residual of homogeneous plastic deformation is between 10% and 20% of said deformation. In other words, the ratio D2 / D1 is between 0.1 and 0.2. Overall, the geometry of the remaining ball unchanged due to its hardness greater than that of parts 1B and 1C, the deformations of the edges 25B and 25C have the shape of cap slices spherical bounded between two planes parallel to the planes of the faces of contact 1B 'and 1C'.

In the example of FIGS. 2A to 2C, the geometries of the holes 20B and 20C are the same, and it is assumed that parts 1 B and 1C have substantially the same hardness. As a result, deformations of edges 25B and 25C are substantially the same amplitude and distance of penetration of the ball in each of holes 20B and 20C is the same. If we chose pieces of different hardnesses, the ratio between the penetration distances of the shear member in each of the two holes would be inversely proportional to the hardness ratio.

FIG. 3 shows an alternative embodiment, in which the two holes have different dimensions. We consider for example that the hole 20B made in the part 1B is unchanged. Drilling 120C which is practiced in the part 1C present, like the drilling 20C, a frustoconical portion 124C located on the side of the contact face 1C 'and a cylindrical portion 126C located on the opposite side, as well as an edge 125C connecting these two portions. However, compared to FIGS. 2A to 2C, the diameter D 'of the cylindrical part 126C has been reduced, while the angle at the top of the cone delimited by the frustoconical portion 124C has been open. Thus, the homogeneous plastic deformation in the region of the ridge 125C extends over part of the frustoconical portion 124C, so that, in the hole 120C, the contact surface between the ball 22 and the wall of the piercing is greater.

We can thus adapt the geometry of the holes to the hardness of the pieces considered. In the examples of FIGS. 2A and 3, the zones of contact between the ball 22 and the walls of the holes have tangency points, respectively 28B, 28C and 128C for the holes 20B, 20C and 120C, to which the contact between the ball and the walls of the drilling is tangential. When, as in the example shown, this contact takes place on the circular edges connecting the frustoconical parts and the cylindrical parts of the holes, these tangent points are located in the central regions of the deformations of these edges. We determine then the contact angles which are the angles, respectively αB, αC and α'C, formed between the spokes of the ball passing through these contact points 28B, 28C and 128C, and the plane P of junction between the contact faces of the parts 1B and 1C. Preferably, these contact angles are between 25 ° and 35 °, so that the deformation does not affect the contact face. As seen in Figure 3, the contact angles α'C and αB are different. In this case, the angle α'C is greater than the angle αB because the diameter D 'is less than diameter D and the height H' between the edge 125C and the plane P is greater than the height H between the edge 25B and the same plan P.

In the example of FIG. 4, the hole 20C made in the part 1C is similar to that of FIGS. 2A to 2C. In this drilling, we also determines the same contact angle αC between the radius of the ball passing through the point of tangency and the plane P.

The drilling 120B which is practiced in the part 1B is different. It indeed has a blocking section with which the shear, in this case the ball 22, cooperates by being wedged in this drilling. Thus, before the assembly between parts 1B and 1C, the ball 22 is forcibly engaged in drilling 120B. Of course, several fixing assemblies being provided, it is desirable that the balls of all these sets are arranged in the same way in the holes in the same part. To assemble the parts 1B and 1C, it suffices then approach the part 1C and exercise the axial stresses sufficient to achieve, at least in the drilling of this part, the desired deformations. Depending on the respective hardness of the two parts, these deformations can also affect the 120B drilling on the other room. In both cases, we make sure that the deformations remain in the field of homogeneous plastic deformations, for have a residual elasticity allowing reassembly without play.

Advantageously, the wedging surface of the ball in the 120B hole is formed by a surface which is oriented parallel to axis A with respect to which the torque to be transmitted is determined between parts 1B and 1C and which is parallel to the axis A 'of alignment of the holes indicated in figure 4. For example, as in the example shown, the bore 20B has a single cylindrical portion 126B, which opens on the contact face 1B ', and whose diameter is very slightly less than the diameter of the ball 22. Thus, the contact forces between the ball and the wedging surface are oriented purely radially, so that the ball remains stuck in its bore 120B without having a tendency to be expelled from it. In this case, the distances D1 and D2, mentioned previously with reference to FIGS. 2B and 2C, are appreciated when the ball is stuck in its housing 120B.

The geometry of the holes is advantageously provided for so that the contact zones between the shearing member (in the ball) and the walls of these holes are located at vicinity of the contact plane P while being slightly spaced from this last, so as not to affect the flatness of the contact faces 1B 'and 1C'. For example, when the holes include a frustoconical part and a cylindrical part, the H / D ratio previously mentioned makes it possible to fulfill this condition.

Advantageously, as can be seen in FIG. 1, the drilling of the fastening assemblies in rotation are carried out at vicinity of the outer periphery of the contact face of at least one parts, in this case, the two holes are made near the substantially similar outside diameter of parts 1B and 1C. By locating the fastening assemblies in rotation as far as possible from the axis of rotation A, the transmission of a torque which is all the more significant by these sets. Likewise, the brake cover part 1D has a diameter less than the maximum diameter of part 1C, but we see that the rotational securing assembly 30 is located in the vicinity of the outer periphery of this 1D brake cover part.

For convenience of description, partially shown in Figures 2A to 4 parts 1B and 1C. It is obvious that the rotational securing assembly described with reference to these figures can also be the assembly 30 for rotation between the parts 1C and 1D. We can choose that all the joining sets in rotation are identical, or that some of them are different, retaining for example one of the variants of FIGS. 2A to 4 described above.

Claims (14)

1. Hydraulic device such as a motor or a pump comprising a first piece (1C) formed by a part of the casing in which a cylinder block (2) is arranged and a second piece (1B; 1D) fixed to this first piece, the device comprising a system for rigidly attaching the two pieces in rotation so as to allow passage of a torque between these pieces, the latter each having a contact face (1C', 1B'; 1C", 1D"), the two contact faces being held one against the other by means (14, 15) applying an axial stress, the said system including at least two assemblies for rigid attachment in rotation (20; 30) each comprising two aligned bores (20B, 20C; 20B, 120C; 120B, 20C) respectively formed in each of the two pieces (1B, 1C; 1C, 1D) and opening in their respective contact faces, and a shear part (22) extending in these bores, the shear parts being able to withstand the shear forces generated by the transmitted torque,
   characterised by the fact that for each assembly for rigid attachment in rotation (20, 30), the shear part (22) and the bores (20B, 20C; 20B, 120C; 120B, 20C) have respective dimensions in the free state not allowing contact between the said contact faces(C', 1B'; 1C", 1D") when the shear part is arranged in the bores, and by the fact that, for each assembly for rigid attachment in rotation (20, 30), the shear part co-operates with the bores without clearance and at least one of the elements formed by the two bores and by the shear part presents, as a result of the application of the said axial stress to the pieces, a deformation in the domain of homogeneous plastic deformations, the said deformation affecting a zone which is situated in the vicinity of but outside the plane (P) of contact between the contact surfaces.
2. Device as described in claim 1, characterised by the fact that the shear parts comprise ball bearings (22).
3. Device as described in claim 1 or 2, characterised by the fact that the walls of the bores (20B, 20C; 20B, 120C; 120B, 20C) and the shear parts (22) are formed of materials which have different hardnesses.
4. Device as described in claim 3, characterised by the fact that the walls of the bores (20B, 20C; 20B, 120C; 120B, 20C) are formed of a material which has a lesser hardness than that of the material of which the shear parts (22) are formed.
5. Device as described in any one of claims 1 to 4, characterised by the fact that at least one of the bores (20B, 20C; 120C) of at least one assembly for rigid attachment in rotation (20, 30) has a part in the form of a truncated cone (24B, 24C; 124C) with which the shear part (22) co-operates.
6. Device as described in claim 5, characterised by the fact that at least one of the bores (20B, 20C; 120C) of at least one assembly for rigid attachment in rotation (20, 30) has a cylindrical part (26B, 26C; 126C) and a part in the form of a truncated cone (24B, 24C; 124C) joined by a circular ridge (25B, 25C; 125C), the said part in the form of a truncated cone being on the side of the contact face (1B', 1C') of the piece in which the bore in question is formed, and by the fact that the shear part (22) is in contact with this ridge.
7. Device as described in claim 6, characterised by the fact that the circular ridge is situated at an axial distance (H, H') from the contact face of the piece (20B, 20C) in which the bore in question is formed which is between 15% and 40% and preferably between 20% and 30% of the diameter (D, D') of the said cylindrical portion.
8. Device as described in claim 2 and any one of claims 1 to 7, characterised by the fact that, for each assembly for rigid attachment in rotation (20, 30) for which the shear part (22) is formed by a ball bearing, the zones of contact between the ball bearing and the walls of the bores have points of tangency (28B, 28C; 128B) at which the contact is tangential, and the radii of the ball bearing passing through these points of tangency are inclined relative to the joining plane (P) between the contact faces of the pieces at angles (αB, αC; α'C) called "angles of contact" of between 25° and 35°.
9. Device as described in claim 8, characterised by the fact that the angles of contact (αB, α'C) are different for the two pieces (1B, 1C).
10. Device as described in any one of claims 1 to 9, characterised by the fact that one (120B) of the bores (120B, 20C) of at least one assembly for rigid attachment in rotation has a locking section (126B) with which the shear part (22) co-operates by being wedged in the bore.
11. Device as described in claim 10, characterised by the fact that the said locking section presents an axial locking surface (126B).
12. Device as described in any one of claims 1 to 11, characterised by the fact that the bores ((20B, 20C, 120B, 120C) are formed in the vicinity of the external periphery of the contact face of at least one of the pieces.
13. Device as described in any one of claims 1 to 12, characterised by the fact that the second piece is formed by a part (1D) of the casing of a brake in which braking means (9) are arranged for the motor or the pump.
14. Device as described in any one of claims 1 to 12, characterised by the fact that the second piece (1B) is formed by a part of the casing of the hydraulic motor or of the pump in which the cylinder block (2) is arranged, this second piece presenting on its internal periphery the reaction cam for the pistons (2') of this cylinder block.

Images