EP1466093B1 - Hydraulic radial piston motor - Google Patents

Description

The present invention relates to a radial piston hydraulic motor as defined in the preamble of claim 1 comprising a cam and a cylinder block able to rotate relative to each other about an axis of rotation, the block cylinders having radial cylinders connected by cylinder ducts to communication ports located in a communication face of the cylinder block which is perpendicular to the axis of rotation, pistons slidably mounted in the cylinders being adapted to cooperate with the cam , the latter having several lobes each having two ramps, the motor further comprising a fluid dispenser having a dispensing face which is perpendicular to the axis of rotation and which is able to bear against the communication face of the cylinder block, this distribution face having dispensing orifices comprising orifices capable of being connected to a fluid supply and orifices adapted to be connected to a fluid outlet, the fluid distributor being rotatably connected to the cam so that a ramp of the cam corresponds to each dispensing orifice, said dispensing orifices being able to communicate with each other; after the others with the communication ports during the relative rotation of the cylinder block and the distributor. Such an engine is known, see each of US-A-4522110 or DE-A-10033264 or DE-C-829553 or DE-A-2634065 or FR-A-2587761 or EP-A-0935069.

For an engine of this type, operating at full displacement, each communication orifice is successively opposite a dispensing orifice connected to the fluid supply and facing a dispensing orifice connected to the fluid outlet. . The connection to the dispensing orifice which is connected to the supply has the effect of pushing radially outwardly the piston contained in the cylinder connected to the communication port in question, while the connection of the same communication port to a dispensing orifice connected to the fluid outlet makes it possible to retract this piston into its cylinder, towards the axis of the engine. Thus, each piston cooperates successively with the different parts of the lobes of the cam to allow the relative rotation of the cylinder block and the cam.

The spacings between the dispensing orifices and the spacings between the communication orifices are such that a communication orifice is not simultaneously connected to two dispensing orifices respectively connected to the fluid supply and to the fluid outlet.

During the relative rotation of the cylinder block and the distributor, the working chambers of the cylinders, that is to say the parts of these cylinders defined below the pistons, are alternately placed at the high pressure and the low pressure. In these working chambers, therefore, pressure changes generally take place at a very rapid rate. These pressure changes subject the pistons to proportional forces, and these forces are transmitted by the pistons to the cam.

As a result, the engine components, in particular the crankcase, are subjected to load variation which causes noise-generating vibrations, the intensity of the noise produced being mainly dependent on the speed of the increase and the pressure drops in the crankcase. working rooms.

For the motor to function properly, the pressure difference between the fluid supply and the fluid outlet is important. When a piston contributing to the engine torque reaches the end of its stroke, towards its position farthest from the axis of the engine (top dead center), because of the connection of the port of communication of its cylinder to an orifice The same communication port is isolated from the dispensing port connected to the fluid supply, and is then connected to another dispensing orifice which, this time, is itself connected to the fluid outlet. This results in a phenomenon of expansion in the cylinder of the piston in question, the fluid present at a high pressure in this cylinder being suddenly brought into communication with a significantly lower pressure, which is that of the fluid exhaust. Conversely, when the piston has reached the bottom dead center of its stroke (its position closest to the axis of the engine), its cylinder is isolated from the fluid outlet and is then connected to the fluid supply. to allow a new centripetal stroke of the piston. At this moment, the fluid contained in the cylinder passes from a low pressure to a much higher pressure which is that of the fluid supply. A relaxation phenomenon also occurs, from the supply of fluid, to the cylinder. In the previous case, the expansion occurs from the cylinder to the fluid outlet.

In both cases, the detents that occur are generating shock or shock sensations, and noises such as clicks.

These phenomena become even more sensitive as the quality of the engines has been improved and leaks have been reduced in these engines. Indeed, in old engines, the leaks that reigned there allowed to avoid abrupt pressure variations between the different speakers.

To avoid, or at least to limit the phenomena of shocks due, in particular, the too fast detents of the fluid contained in the working chambers of the cylinders when the communication conduits are placed in communication, through the dispensing orifices, with the supply of fluid, it is possible to equip the edge of the dispensing orifices with at least one notch capable of establishing (see each of US-A-4522110 or DE-A-10033264 or DE-C-829553 or DE -A-2634065 or FR-A-2587761 or EP-A-0935069), during the relative rotation of the cylinder block and the distributor, a small section of communication between the working chambers of the cylinders and the distribution ducts. This small communication section, open for a very short time, makes it possible to avoid excessive pressure variations in the working chambers.

The plaintiff company has however found that this solution is not always easy to implement. Indeed, in some cases, the making of the notches on the edges of the dispensing orifices is not easy and / or expensive.

Therefore, the invention aims to provide an alternative solution to avoid or limit the aforementioned shock phenomena.

This object is achieved by the fact that the edges of at least some communication ports each have at least one notch capable of establishing a small communication section with a dispensing orifice.

The invention finds a particularly advantageous application for engines in which the ratio of the number of cylinders to the number of cam lobes is close to 1. Indeed, a radial piston hydraulic motor comprises a dispensing orifice for each of the ramps. its cam lobes, that is to say it has twice as many dispensing orifices as cam lobes. The engine however comprises a communication port for each cylinder. Therefore, when the aforementioned ratio is close to 1, the engine has about twice as many distribution orifices than communication ports. The fact of making the cuts on the edges of the communication ports is therefore significantly less expensive than would be the realization, for the same type of engine notches on the edges of the dispensing orifices.

As will be seen in the following, the invention covers the case where the edge of each communication orifice has at least one notch, such as one where only some of these orifices have their edges provided with at least one notch.

This being the case, in one or the other case, for the same technical effect and for an engine in which the ratio of the number of cylinders to the number of cam lobes is close to 1, the number of communication orifices in front of be provided with notches and significantly less than the number of dispensing orifices to be.

The dimensions of the notches are chosen to allow, through these notches, during the relative rotation of the cylinder block and the fluid distributor, the gradual passage of a volume of fluid between the orifices at different pressures, said volume of corresponding pressure compensation, for given operating pressures and rotational speeds, to the decompression or expansion of the maximum volume of the working chamber, obtained at the top dead center of the piston on the cam. The passage of a volume of pressure compensation fluid through the restriction that constitutes a notch, before the open communication between the communication orifice and a dispensing orifice is established, allows to gradually vary the pressure of the pressure. fluid to the communication port to gradually bring it to the pressure of the fluid at the dispensing orifice. The length of time during which a notch allows the passage of fluid between the communication orifice and the dispensing orifice during the rotation of the cylinder block and the distributor depends on the speed of rotation of the engine. This is why the operating pressures and the speed of rotation are parameters to be taken into account in the definition of the notch.

The edge of each communication port comprises a leading portion through which the communication between the communication port and the dispensing orifices opens during relative rotation between the cylinder block and the distributor in a direction of rotation. relative given, as well as a separation portion through which the communication between the communication port and the dispensing orifices closes during the relative rotation between the cylinder block and the distributor in the same direction of relative rotation.

According to an advantageous variant, particularly suitable for motors having two operating directions, at least some communication orifices have a leading portion and a separating portion each having a notch capable of establishing a small communication section with a dispensing orifice. .

The applicant company has found that the notches are particularly useful when the communication between the dispensing orifices and the communication orifices opens because, at this moment, the pressure of the fluid contained in the working chambers and that of the fluid contained in the distribution ducts (whether the supply pressure or the exhaust pressure) are significantly different and it is this pressure difference which, if the opening of the distribution ports is too abrupt, is generator of shocks and noises. In other words, the presence of the notches is particularly desirable on the leading portions of the communication ports. In some applications, the motor always or almost always rotates in the same direction of rotation. This is for example the case when it is used to drive mills, conveyor belts or concrete mixers. In this case, it may be sufficient that only the portions of the edges of the communication orifices which, in this direction of rotation, form the leading portions of these edges, bear notches.

In other applications, the motor is reversible, in two opposite directions of rotation. This is for example the case when used to drive a turret shovel. In this case, two opposite portions of the edges of the communication orifices may, depending on the direction of rotation of the motor, be a leading portion or a separation portion. It is therefore desirable that these two portions are each provided with a notch.

In many applications, the motors are reversible and have no preferential direction of operation. This is for example the translation of certain types of gear, particularly crawler gear.

In this case, advantageously, the notches of the leading portions and separation of the edges of said communication orifices are symmetrical.

Some reversible motors have a preferred direction of operation. For example, machine translation engines can operate primarily at high speed in the forward direction while speed is limited in reverse. In this case, it is possible to provide large cuts on the portions of the edges of the communication ducts which are the leading portions in the preferred direction and small notches on the opposite portions of these edges, which are the separation portions in this case. preferential direction and the leading portions in the opposite, non-preferential direction.

The large notches allow communication sections with the dispensing ports which are larger than those allowed by the small notches, for example in proportion to the ratio between the highest speeds of rotation of the motor respectively allowed in the preferential sense and respectively in the non-preferential sense of the latter.

According to an advantageous variant, in which each ramp of the cam comprises a convex portion and a concave portion, two adjacent ramps being interconnected either by a cam crown area extending between their respective convex regions, or by a zone of cam bottom extending between their respective concave regions, said areas of cam peaks and cam bottom are substantially circular arcs centered on the axis of rotation, so that when the pistons cooperate with said zones, their Radial strokes are substantially zero. Then, the dispensing orifices and the communication orifices advantageously have dimensions such that, during the relative rotation of the cylinder block and the distributor, each dispensing orifice remains momentarily isolated from any communication orifice.

The cam and cam bottom regions are substantially circular arcs centered on the axis of rotation, which means that the radii of curvature of these zones, measured between their ends, are substantially equal, for the zones of cam end at the minimum radial distance from the cam to the axis of rotation and, for the cam bottom areas, to the maximum radial distance from the cam to the axis of rotation. The radius of curvature of said zones may, however, be different from the minimum radius and the maximum radius of this cam, but, overall, their distances to the axis of the motor are respectively substantially equal to these minimum and maximum radii. When a piston cooperates with such zones, its radial stroke is substantially zero, which means that this stroke is zero or that it is at most of the order of approximately 0.5% of the maximum amplitude of the stroke of the piston. Thus, the cam top areas and the cam bottom areas do not contribute to the engine torque. They cover the weak angular sectors, for example of the order of 2 to 3 °, and they make it possible, during the relative rotation of the cylinder block and the distributor, to provide dead-time instants for each piston (neutral position). high for cam bottom zones and bottom dead center for cam top regions), during which the pressure in the working chamber of the cylinder in which the cam moves piston considered can, by the volume of compensation fluid passing through a notch, equal or approach the pressure of the dispensing orifice.

It is particularly advantageous that the lapse of time during which a given communication port is in communication with a dispensing orifice only by the notch that the edge of this communication port has, be located within the time period during which wherein the piston fed by this communication port cooperates with either a cam-top region or with a cam bottom area. It is indeed advantageous to use this moment during which the piston does not develop a torque to gradually vary the pressure in the working chamber through the notch of the edge of the communication port.

Advantageously, the angular sectors covered by a cam-top region and by a cam bottom zone are substantially equal to each other, and substantially equal to 2 to 3 °.

The invention will be better understood and its advantages will appear better on reading the detailed description which follows, of an embodiment shown by way of non-limiting example.

• la figure 1 est une vue en coupe axiale d'un moteur auquel l'invention peut être appliquée ;
• la figure 2 est une vue partielle en coupe radiale selon la ligne II-II de la figure 1 ;
• la figure 3 est une section prise selon l'arc de cercle III-III de la figure 2 ; et
• les figures 4 et 5 montrent, en coupe radiale partielle, deux variantes de réalisation.

The description refers to the accompanying drawings in which:

• Figure 1 is an axial sectional view of a motor to which the invention can be applied;
• Figure 2 is a partial view in radial section along the line II-II of Figure 1;
• Figure 3 is a section taken along the arc III-III of Figure 2; and
• Figures 4 and 5 show, in partial radial section, two embodiments.

FIG. 1 shows a hydraulic motor comprising a fixed casing in three parts, 2A, 2B and 2C, assembled by screws 3.

Of course, the invention is not limited to hydraulic motors with fixed housing, but it also applies to hydraulic motors with rotating housing which are well known to those skilled in the art.

Part 2C of the housing is closed axially by a 2D radial plate also fixed by screws. A corrugated reaction cam 4 is formed on the part 2B of the housing.

The engine comprises a cylinder block 6 which is mounted relative to rotation about an axis of rotation 10 with respect to the cam 4 and which comprises a plurality of radial cylinders which can be supplied with fluid under pressure and within which the radial pistons 14 are slidably mounted.

The cylinder block 6 rotates a shaft 5 which cooperates with it by splines 7. This shaft carries an outlet flange 9.

The engine further comprises an internal fluid distributor 16 which is secured to the housing with respect to the rotation about the axis 10. Between the distributor 16 and the internal axial face of the part 2C of the housing are formed grooves of distribution, respectively a first groove 18, a second groove 19 and a third groove 20. The distribution ducts of the distributor 16 are distributed in a first group of ducts which, like the conduit 21, are all connected to the groove 18, a second group of ducts (not shown) which are connected to the groove 19 and a third group of ducts which, like the duct 22, are connected to the groove 20. The first groove 18 is connected to a first main duct 24 to which are connected all the dispensing orifices of the distribution ducts of the first group, such as the orifice 21A. The third groove 20 is connected to a second main duct 26 to which are thus connected all the distribution orifices of the ducts of the third group, such as the orifice 22A of the duct 22.

Depending on the direction of rotation of the motor, the main ducts. 24 and 26 are respectively an exhaust duct and a fluid supply duct, or vice versa.

The distribution ducts open into a distribution face 28 of the distributor 16, which bears against a communication face 30 of the cylinder block. Each cylinder 12 has a cylinder duct 32 which opens into this communication face so that, during the relative rotation of the cylinder block and the cam, the cylinder ducts are alternately in communication with the distribution ducts of the different groups.

The engine of FIG. 1 further comprises a device for selecting the displacement, which in this case comprises a bore 40 which extends axially in the part 2C of the casing and in which is disposed an axially movable selection slide 42 . The bore 40 comprises three communication channels, respectively 44, 46 and 48, which are respectively connected to the grooves 18, 19 and 20, by connecting conduits, respectively 44 ', 46' and 48 '. The drawer 42 is movable between two extreme positions inside the bore 40 in which it makes the channels 44 and 46 communicate or the channels 46 and 48 through its groove 43.

When the slide 42 is in its position of FIG. 1, the grooves 19 and 20 communicate, so that the dispensing orifices connected to them are at the same pressure, different from that of the dispensing orifices connected to the groove 18. When the drawer is moved in the direction of the arrow F, it is the distribution orifices connected to the grooves 18 and 19 which are put at the same pressure, different from that to which the orifices connected to the groove 20 are put.

FIG. 2 shows a cam lobe, with its two ramps, respectively 50 and 50 '. These two ramps each represent a convex portion, respectively 51 and 51 ', and a concave portion, respectively 52 and 52'. The convex portions are those closest to the axis of rotation of the motor, while the concave portions are those which are the furthest away. A piston 14 cooperates with the cam-top region 58, through which the concave portions 52 and 52 'of the ramps 50 and 50' meet. This piston is in its position of top dead center, that is to say that the volume of the working chamber of the cylinder in which it moves is then maximum. Other pistons, 14 'and 14 ", cooperate with other areas of the cam.

At this time, for the reasons described below, the communication port 32A, by which the cylinder in which the piston 14 moves can be supplied with fluid under pressure, and by which the fluid contained in this cylinder can escape, is isolated from any dispensing orifice.

For clarity of explanation, it has in fact shown in Figure 2 two distribution orifices, respectively 21A and 23A, for example respectively connected to the grooves 18 and 19, although they are normally not visible on the cut . The positions of two other communication ports, namely 32'A and 32'A, have also been indicated.

The communication ports of Figure 2 are all identical and each have two notches, respectively 54A and 54B, adapted to establish a small communication section between the communication port equipped with said notches and the dispensing orifices.

If it is considered that the cylinder block moves relative to the distributor in the direction of rotation R1, the portion B1 of the edge of the communication port 32A on which the notch 54A is made is a driving portion, that is to say that it is through this portion that opens the communication between the communication port 32A and the dispensing orifice 21A. Thus, at first, this communication is established solely by the notch 54A, for a relative rotation angle of the distributor and the cylinder block equal to the angular amplitude α1 covered by the notch 54A. With the notch 54A, the communication between the communication port 32A and the dispensing orifice 21A opens gradually, so that the pressure in the working chamber of the cylinder in which the piston 14 moves and the pressure in the distribution duct which opens to the dispensing orifice 21A can be gradually balanced. When the rotation continues, the communication opens widely, as the orifices 32A and 21A overlap angularly.

For the rotation of the cylinder block in the direction R1 relative to the distributor, the portion B2 of the edge of the communication port 32A which is opposite the portion B1, constitutes a separation portion, through which the communication between the orifice 32A communication and 23A distribution port closes.

When, on the other hand, the direction of rotation of the motor is reversed so that the cylinder block rotates relative to the distributor in the direction of rotation R2, it is this time the portion B2 of the edge of the communication orifice which constitutes a portion of attack. In this case, the communication between the communication port 32A and the dispensing orifice 23A opens by the notch 54B. The pressures in the working chamber of the cylinder in which the piston 14 moves and in the distribution pipe that opens to the dispensing orifice 23A can then be equilibrated more gradually than in the prior art, in which the orifices of communication were devoid of nicks.

Thus, in the direction of rotation of the motor, one or the other of the notches 54A and 54B is useful in order to avoid, or at least to limit, the phenomena of shock during the setting in communication too fast of two enclosures in which different fluid pressures prevail.

In the example of Figure 2, the notches 54A and 54B are symmetrical with respect to a diameter D of the communication port 32A passing through the axis of rotation 10 of the motor. This is also seen in the section of Figure 3. As indicated above, it could however be expected that the notches are not symmetrical. In particular, if the direction of rotation R1 of the cylinder block relative to the distributor corresponds to the preferential direction of operation of the engine and if, in its non-preferential direction, the speed is less than that which can be reached by the preferential direction, then the notch 54A may be larger than the notch 54B.

The cam crown zone 56 and the cam bottom zone 58 respectively extend over angular sectors α ₅₆ and α ₅₈ , measured between spokes passing through the axis of the motor, which are substantially equal to each other and equal to about 2 to 3 °.

Advantageously, in order to take advantage of the cam bottom regions and the cam top regions to balance the pressures between the working chambers of the cylinders and the supply or exhaust ducts of the motor, it is chosen that the lapse of time during which the communication between a communication orifice and a dispensing orifice is effected by a notch either within the lapse of time during which the piston of the cylinder fed by this communication orifice cooperates with a bottom or top region of a cam . We take advantage of the moments when the pistons do not contribute to the engine torque to balance the pressures.

For example, with an angular sealing sector α ₂ between the duct 21A and the duct 32A, it is chosen that α ₅₈ = 2 (α ₁ + α ₂ ), the cam bottom area being symmetrical with respect to a radius R which determines an axis of symmetry for the cam lobe which includes the ramps 50 and 50 '; the angular sealing sector α ₂ and the angular coverage of a notch α ₁ to be appreciated, for a direction of rotation, with respect to a half-zone of cam bottom. The same remark can be made about the cam vertex area 56 which is symmetrical with respect to the radius RS.

One can choose that, except for the presence of the notches, the communication orifices are circular. In such a case, the notches can be made by a displacement, in a diametral plane of the communication orifice, of a bur which slightly cuts the edges of this orifice. To make symmetrical cuts, a diameter of the cutter can be coaxial with that of the communication orifice, while to connect the dissymmetrical notches, the diameter of the cutter can be slightly offset from that of the communication orifice. .

In the example of FIG. 4, the communication orifice 132A has, like the orifice 32A, a driving portion B1 and a separating portion B2, when the cylinder block rotates relative to the distributor in the direction of rotation R1. However, it is found that, for the orifice 132A, the leading portion B1 and the separating portion B2 are generally convex, seen from inside the orifice. In fact, with the exception of the notches 154A and 154B, the leading and separating portions substantially form arcs of circles capable of covering the edges of the dispensing orifices 21A and 23A during the relative rotation of the cylinder block to the distributor. The shape of the communication orifice is substantially complementary to that of the distribution orifices 21A and 23A.

If it is considered that the cylinder block rotates in the direction of rotation R1 with respect to the distributor, then the communication between the communication orifice 132A and the distribution orifice 21A begins with the notch 154A which, as indicated above , establishes a small communication section to gradually balance the pressures in the respective speakers connected to the dispensing orifice and the communication port. However, as soon as the relative angle of rotation between the cylinder block and the distributor is sufficient, the leading portion B1 of the communication orifice exceeds the edge D1 of the dispensing orifice, in the direction R1 and, from this situation, the overlap section between the communication orifice and the dispensing orifice increases very rapidly depending on the relative rotation angle between the cylinder block and the distributor. In other words, as soon as the pressure between the speakers respectively connected to the communication orifice and to the dispensing orifice has been relatively balanced by the small communication section authorized by the notch 154A, the communication between the orifices 132A and 21A can increase very quickly, with very low pressure drops. Thanks to the notch, it avoids or at least limits the shock phenomena and, thanks to the particular shape of the attack portion B1, increases the efficiency of the engine.

If the motor has a single direction of rotation in which the cylinder block rotates in the direction R1 relative to the distributor, then it is not necessary that the partition portion B2 has a shape substantially complementary to the portion D2 of the edge of the orifice 23A through which the communication between the orifices 132A and 23A closes. If, on the other hand, the motor has two operating directions none of which is preferential, then the separating portion B2, which becomes a driving portion in the direction of rotation R2, is advantageously shaped like the portion B1, by symmetry. relative to a line L of symmetry of the orifice 132A passing through the axis of rotation of the motor.

Of course, in the case of a motor having two directions of rotation of which only one is preferential, it can be chosen that only the portions of the edges of the communication orifices which constitute attack portions in a preferred direction, will be formed substantially complementary to the portions of the edges of the dispensing orifices through which the communication between the communication orifices and the dispensing orifices open.

When the dispensing orifices are circular, the communication orifices may have, with the exception of the notches, a shape of the type described in FR-A-2 587 761. Conversely, the dispensing orifices may have such a shape while, without their notches, the communication ports would be circular.

Figure 5 shows another variant, in which the communication port 232A has a substantially elongate shape along a radius of the motors passing through the axis of rotation of the latter. In other words, with the exception of the notches 254A and 254B, the dimension of the orifice 232A measured along a radius of the motor is greater than the dimension of this orifice measured transversely to this radius. Without presenting the relatively complex form of the orifice 132A, the communication orifice 232A has, like the latter, the advantage of allowing a very rapid opening of the communication between the communication orifice 232A and the distribution orifice 21A. or the dispensing orifice 23A, from the moment when the pressure in the enclosures connected respectively to the communication orifice and to the dispensing orifices has been substantially balanced due to the communication being limited by the notch 254A or the notch 254B.

Note in Figure 5 that the notch 254A is larger than the notch 254B, the direction of rotation R1 of the cylinder block relative to the distributor having a preferred direction relative to the opposite direction R2.

In the figures which have just been described, the notches of the communication orifices are substantially arranged on an arc of a circle passing through the axis of rotation of the motor.

According to a variant not shown, one can also choose to have all the notches of the leading portions of the orifices on a first circle centered on the axis of rotation of the engine, and all the notches of the portions of separation of these orifices on a second circle, of different radius from the first.

As indicated above, the engine shown in FIG. 1 has two active operating displacements, a displacement selector making it possible to put certain distribution ducts in communication with each other. Part of the pairs of communication ports consecutive has two orifices placed at the same pressure, so as to operate the engine in small displacement.

There is another way to operate the engine in two different displacements, which is to make some pistons inactive. This type of small displacement control is for example described by the patent application No. FR-A-2 796 992.

In this case, the deactivated pistons are generally declutched, being brought back to the axis of rotation of the engine. Be that as it may, in this situation, only the pistons remaining active contribute to generate a driving torque. In small displacement, for the same flow of fluid delivered by the pump feeding the engine, the latter rotates at a higher speed than it would have for the same flow of fluid in large displacement.

The aforementioned relaxation and shock phenomena are even more sensitive for high speed operation. Thus, according to the invention, it can be provided that only the communication orifices of the piston cylinders which are active in the small displacement cylinder each have at least one notch on the flange. In this case, all the communication ports of these cylinders have a notch, while those of the other cylinders do not have one. Depending on whether the motor is reversible or not, and for the reasons indicated above, it can be provided that the communication orifices that have at least one notch have only one or on the contrary that they have two, used to the opening of the communication between said orifices and the dispensing orifices in each of the two directions of operation of the engine.

In this case, the maximum rotational speed being less important in large displacement than in small displacement, it can be judged that it is not necessary to make notches on the orifices of the cylinders of the pistons which are inactive in small displacement.

In a variant, it is possible to cut the edges of all the communication orifices. However, insofar as the maximum speed in large displacement is lower than the maximum speed in small displacement, it can be provided that the edges of the communication ports of the cylinders whose pistons are active in the small displacement have larger notches than those of the edges of the communication ports of the cylinders of the pistons which are inactive in the small displacement.

Claims (10)

1. A hydraulic motor having radial pistons, and comprising a cam (4) and a cylinder block (6) that are suitable for turning relative to each other about an axis of rotation (10), the cylinder block having radial cylinders (12) connected via cylinder ducts (32) to communication orifices (32A; 132A; 232A) situated in a communication face (30) of the cylinder block that is perpendicular to the axis of rotation, pistons (14) mounted to slide in the cylinders (12) being suitable for co-operating with the cam, which cam is provided with a plurality of lobes, each of which has two ramps (50, 50'), the motor further comprising a fluid distributor (16) having a distribution face (28) that is perpendicular to the axis of rotation and that is suitable for being in abutment against the communication face (30) of the cylinder block, said distribution face being provided with distribution orifices (21A, 23A) comprising orifices suitable for being connected to a fluid feed (26) and orifices suitable for being connected to a fluid discharge (24), the fluid distributor (16) being constrained to rotate with the cam (4), so that there is one ramp of the cam that corresponds to each distribution orifice, said distribution orifices being suitable for communicating one after another with the communication orifices (32A; 132A; 232A) while the cylinder block (6) and the distributor (16) are turning relative to each other;
   said hydraulic motor being characterised in that the edge of each of at least certain communication orifices (32A; 132A; 232A) is provided with at least one notch (54A, 54B; 154A, 154B; 254A, 254B) suitable for establishing a small section of communication with a distribution orifice (21A, 23A).
2. A motor according to claim 1, in which the edge of each communication orifice (32A; 132A; 232A) has a leading portion (B1) via which communication between the communication orifice and the distribution orifices (21A, 23A) opens while the cylinder block (6) and the distributor (16) are turning relative to each other in a given direction of relative rotation (R1), and a trailing portion (B2) via which communication between the communication orifice and the distribution orifices closes while the cylinder block and the distributor are turning relative to each other in the same direction of relative rotation, said motor being characterised in that each leading portion and each trailing portion (B1, B2) of at least certain communication orifices (32A; 132A; 232A) has a notch (54A, 54B; 154A, 154B; 254A, 254B) suitable for establishing a small section of communication with a distribution orifice (21A, 23A).
3. A motor according to claim 2, characterised in that the notches (54A, 54B) in the leading portion (B1) and in the trailing portion (B2) of the edge of each of said communication orifices (32A) are symmetrical.
4. A hydraulic motor according to claim 2, the motor having two directions of rotation (R1, R2), one of which directions (R1) is a preferred direction, said hydraulic motor being characterised in that those portions of the edges of said communication orifices (132A; 232A) which, in the preferred operating direction, constitute respectively the leading portions (B1) and the trailing portions (B2) are provided respectively with large notches (154A; 254A) and with small notches (154B; 254B).
5. A hydraulic motor according to any one of claims 1 to 4, in which the edge of each communication orifice (132A) has a leading portion (B1) via which communication between the communication orifice and the distribution orifices (21A, 23A) opens while the cylinder block (6) and the distributor (16) are rotating relative to each other in a given direction of relative rotation (R1), and a trailing portion (B2) via which communication between the communication orifice (132A) and the distribution orifices (21A, 23A) closes while the cylinder block and the distributor are rotating relative to each other in the same direction of relative rotation, said hydraulic motor being characterised in that, for at least certain communication orifices (132A), at least the leading portion (B1) has a shape that is substantially complementary to the shape of the portions of the edges of the distribution orifices (21A, 23A) via which the communication between the communication orifices and the distribution orifices opens.
6. A motor according to claim 5, in which the distribution orifices (21A, 23A) are substantially circular, said motor being characterised in that, for at least some of the communication orifices (132A), the leading portion (B) of the orifice has a convex shape as seen from the inside of the orifice.
7. A motor according to claim 6, characterised in that, for at least some of the communication orifices (132A), the leading portion and the trailing portion (B1, B2) are substantially convex, as seen from inside the orifice.
8. A motor according to any one of claims 1 to 7, characterised in that each ramp (50, 50') of the cam has a convex portion (51, 51') and a concave portion (52, 52'), two adjacent ramps being connected together either via a cam crest zone (56) extending between their respective convex regions, or via a cam trough zone (58) extending between their respective concave regions, in that said cam crest zone (56) and said cam trough zone (58) are substantially circular arcs centred on the axis of rotation (10), so that when the pistons (14) are co-operating with said zones, their radial strokes are substantially zero, and in that the distribution orifices (21A, 23A) and the communication orifices (32A; 132A; 232A) have dimensions such that, while the cylinder block and the distributor are rotating relative to each other, each distribution orifice remains momentarily isolated from any communication orifice.
9. A motor according to any one of claims 1 to 8, the motor having two active operating cubic capacities, namely a large cubic capacity in which all of the pistons are active, and a small cubic capacity in which only certain pistons (14) are active, said motor being characterised in that only each of the communication orifices of the cylinders of the pistons that are active in the small cubic capacity is provided with a notch in its edge.
10. A motor according to any one of claims 1 to 8, the motor having two active operating cubic capacities, namely a large cubic capacity in which all of the pistons (14) are active, and a small cubic capacity in which only certain pistons are active, said motor being characterised in that the edges of all of the communication orifices have at least one notch each, and in that the edges of the communication orifices of the cylinders of the pistons that are active in the small cubic capacity have notches that are larger than the notches in the edges of the communication orifices of the cylinders of the pistons that are inactive in the small cubic capacity.

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