Patent Grant
7340988
The present invention relates to a hydraulic machine having axial pistons, such as a motor or a pump, comprising:
GB 1,140,167 discloses a machine of that type, in which the synchronization system comprises a drive part that is stationary relative to the sliding disk and that, for each coupling rod, presents a recess through which the coupling rod passes, said recess being in the form of a radial slot that is open onto the outer periphery of the drive part. While the cylinder block is rotating, the coupling rod that passes through a recess comes intermittently into contact with the faces of the slot that forms the recess, thereby making it possible to hold said rod in a position such that its axis is approximately contained in a normal radial plane, containing the second axis of rotation and a radius extending from said axis and passing through the center of the second spherical joint corresponding to said rod. Thus, the axis of each coupling rod is held approximately in a normal radial plane, so that the rotation of the sliding disk about the second axis of rotation is synchronized with the rotation of the cylinder block about the first axis.
The time taken for synchronization, between the moment when, under the effect of the cylinder block rotating, a coupling rod tends to depart from a position in which its axis is contained in the normal radial plane that contains the center of its second spherical joint and the moment when such departure is countered by the contact between the rod and a face of the slot, thereby holding the axis of said rod approximately in said normal radial plane, is a function of the respective dimensions of the slot and of the rod engaged therein. More precisely, said time depends on the reference clearance between the first drive surface formed on the rod and the second drive surface formed by the wall of the slot, said reference clearance being the clearance that is measured between said surfaces when the axis of the coupling rod is in its normal radial plane.
In GB 1,140,167, the slots in the drive part serve to accommodate the tangential movements of the coupling rods, but, insofar as said slots are open onto the outer periphery of the drive part, said tangential movements are not limited when the radial movements increase.
In the description below, the tangential direction is considered to be the direction that is tangential to the circle described by the centers of the second spherical joints whereas the radial direction is the direction that is radial relative to said circle.
Patent Application PCT/EP2004001560 (published as WO2005/078238) discloses a synchronization system in which the first and second drive surfaces are each formed by rotating a generator line about an axis and are thus “surfaces of revolution” or “rotational surfaces”. As is explained in that patent application, this feature makes it possible to reduce the synchronization times by limiting the distance between a first drive surface and the corresponding second drive surface.
As indicated above, the synchronization system serves to hold the axis of each coupling rod approximately in its normal radial plane, i.e. to ensure that the centers of the second spherical joints are positioned correctly and to reduce the forces acting on the coupling rods.
For each coupling rod, clearance is necessary between the first drive surface and the second drive surface. While the cylinder block is rotating, the coupling rod tends to pivot relative to the center of the first spherical joint. This tendency to pivot results from the fact that the second axis of rotation is inclined relative to the first axis of rotation. The centers of the first spherical joints are disposed on a first circle centered on the first axis of rotation and contained in a plane perpendicular to said axis, whereas the centers of the second spherical joints are disposed on a second circle centered on the second axis of rotation and contained in another plane perpendicular to said axis. Due to the inclination between said axes, the projection of the first circle onto the plane containing the second circle forms an ellipse. As a result, while the cylinder block is rotating, the axis of each coupling rod substantially describes a cone whose vertex is at the center of the second spherical joint, assuming that the axis of the coupling rod is a straight line passing through the centers of the first and second spherical joints.
Thus, while the cylinder block is rotating, the first and second coupling surfaces come intermittently into contact with one another. If it is considered that a coupling rod is initially in a position in which its axis is in its normal radial plane, the rotation of the cylinder block tends to tilt the rod which thus moves away from this initial position until the first drive surface comes into contact with the second drive surface, thus tending to constrain the cylinder block and the sliding disk to rotate together instantaneously, and thus to synchronize them.
The angle between the axis of the coupling rod and the second axis of rotation is designated by angle β below.
With the synchronization system, the aim is for the angle of inclination β of the coupling rods to remain small, while accommodating the angular movements of the coupling rods that are necessary, as indicated above, due to them pivoting relative to the centers of the first spherical joints.
For a coupling rod under consideration, the angle β varies while the cylinder block is rotating. The distance between the second drive surface and the first drive surface is such that said second drive surface comes periodically into contact with the second drive surface, when the angle β reaches a value such that said contact is established. The force exerted by the second drive surface on the first surface during said contact is referred to below as the “synchronization force”.
The synchronization forces depend on the clearance between the drive surfaces, on the angle of inclination of the swash plate, i.e. on the angle of inclination between the second axis of rotation and the first axis of rotation, and on the elasticity of the material of which the coupling rods are made.
An object of the present invention is to improve the above-mentioned state of the art, by proposing a synchronization system making it possible to reduce the synchronization forces, and therefore, to reduce the stresses exerted on the coupling rods.
This object is achieved by means of the fact that the second drive surfaces are off-center relative to the second spherical joints such that a reference amount of clearance between a second drive surface and a first drive surface is small in the zone in which said surfaces come into contact at the time of synchronization in the preferred direction of rotation.
If a particular coupling rod is considered, while the axis of said rod is in its normal radial plane, the reference clearance between the first drive surface associated with said rod and the second drive surface associated with the sliding disk can be seen. If, starting from this situation, the fluid feed to the cylinders is such that the cylinder block rotates in its preferred direction of rotation, said coupling rod tends to tilt relative to the second axis of rotation at the above-mentioned angle β, until synchronization is established for said rod, i.e. until the first drive surface comes into contact with the second drive surface.
In the invention, the second drive surfaces are off-center relative to the second spherical joints, so that said synchronization occurs more rapidly than in the prior art, in which such eccentricity does not exist. Overall, the reference clearance is naturally sufficient to accommodate the necessary movement of the coupling rod, but it is locally small by means of said eccentricity, and synchronization contact is thus established more rapidly, before the angle β reaches a large value, which makes it possible to reduce very significantly the synchronization force at the time of the synchronization.
It should be noted that the invention applies both to synchronization systems using slots having plane side faces as described in GB 1,140,167, and also to synchronization systems in which the drive surfaces are rotational surfaces, as described in PCT/EP2004001560. The invention applies generally to synchronization systems whose drive surfaces have outlines that are closed or open, outlines that are purely rotational, or that locally present flats.
The eccentricity is measured between the geometrical center of a first drive surface and the geometrical center of a second drive surface, in the same plane perpendicular to the second axis of rotation, in a reference position in which the axis of the coupling rod, which axis is a straight line passing through the centers of the spherical joints, is parallel to said axis of rotation. For a surface having constant curvature, the geometrical center is the center of curvature of the curve that said surface forms in section perpendicular to the normal axis, passing through the center of the second spherical joint and parallel to the second axis of rotation. If either of the drive surfaces is not purely a rotational surface, its center is then a center of symmetry.
Advantageously, relative to the second spherical joints, the second drive surfaces present tangential eccentricity measured, for each second spherical joint, tangentially to the circle described by the center of said second spherical joint while the sliding disk is rotating about the second axis of rotation.
The tangential component of the synchronization forces is larger. The eccentricity of the invention, thus preferably includes a tangential component.
Advantageously, relative to the second spherical joints, the second drive surfaces also present radial eccentricity measured, for each second spherical joint, on a radius of the circle described by the center of said second spherical joint while the sliding disk is rotating about the second axis of rotation.
This radial eccentricity is also advantageous, in particular when the drive surfaces are rotational surfaces of the type described in Patent Application PCT/EP2004001560.
Advantageously, the first drive surface and the second drive surface are each defined at least in part by rotating a generator line about an axis.
In a first variant, the first drive surface and the second drive surface are each defined entirely by rotating a generator line about an axis.
This first variant corresponds to the synchronization system described in the above-mentioned PCT Application.
In a second variant, at least one of the first and second drive surfaces presents at least one flat.
In which case, advantageously, the second drive surface is formed by the wall of a radial slot in the sliding disk or in a part that is stationary relative thereto, said slot being open on the side opposite from the second axis of rotation and presenting side faces that are substantially parallel to a radius intersecting the second axis of rotation, and whereas the first drive surface is formed on a lug integral with or secured to a coupling rod and engaged in said slot.
Such radial slots correspond to what is disclosed by GB 1,140,167. It should be noted that the above-mentioned flat is then formed by the side faces of said slots. However, such a flat can also be provided on second drive surfaces of different shapes, e.g. on surfaces having a substantially oval closed outline, with two diametrically opposite flats.
In an advantageous embodiment, the first drive surface is formed on an extension of a coupling rod beyond the second spherical joint, whereas the second drive surface is formed in a setback into which said extension is engaged.
In which case, advantageously, the setback is formed in the same part as the female portion of the second spherical joint and presents an axis of symmetry which is offset relative to the axis of said female portion.
The choice, for the first and second drive surfaces, of an extension to the coupling rod and of a setback is advantageous in that it makes machining and assembly easy. The offset setback can be formed easily by positioning a drill tool correctly. The coupling rod can be circularly symmetrical about its axis, which passes through the centers of the first and second spherical joints.
In another advantageous embodiment, the first drive surface is formed on a coupling rod between the first and second spherical joints, whereas the second drive surface is formed in a recess in a drive part which is stationary relative to the sliding disk, the coupling rod passing through said recess.
The invention will be well understood and its advantages will appear more clearly on reading the following detailed description of embodiments given by way of non-limiting example. The description is given with reference to the accompanying drawings, in which:
The hydraulic machine of
Coupling rods 16 extend between the sliding disk 12 and the pistons 14. More precisely, each coupling rod is connected to a piston via a first spherical joint 16A and to the sliding disk via a second spherical joint 16B. The first spherical joint comprises a female portion 15A recessed into the piston and open on its side closer to the swash plate, and a male head 15B integral with or secured to the coupling rod 16. Similarly, the second spherical joint comprises a female portion 17A recessed into the sliding disk and a male head 17B integral with or secured to the coupling rod 16.
The machine further comprises a shaft 18 which, depending on whether said machine is a pump or a motor, constitutes the inlet or the outlet of the machine. Said shaft is engaged in a bore 2A in the cylinder block, and is constrained to rotate therewith by means of complementary splines 19.
The machine further comprises feed and discharge main ducts 20A, 20B with which cylinder conducts 3A can be put into communication.
The second axis of rotation AS is inclined relative to the first axis AC at an angle α. This angle can be adjustable in order to vary the cubic capacity of the machine. In
The axial bearing 14 is disposed at the end wall of a setback 10B provided in the swash plate, on its side facing towards the cylinder block, and the sliding disk 12 is also disposed in said setback. A retainer part 11 such as a ring segment makes it possible to retain the male heads of the second spherical joints 16B in the female portions of said spherical joints.
If it is considered that the machine is a motor, in view of the feed and of the discharge via the ducts 20A and 20B, the pistons 4 move in translation in the cylinders 3, and this, because of the inclination of the swash plate, causes the cylinder block to rotate. It can be understood that, during this rotation, the centers CA of the first spherical joints are moved over a cylinder having a circular base, whose diameter is D and whose axis is the first axis of rotation AC. At the same time, the centers CB of the second spherical joints are moved over a circle centered on the second axis of rotation AS and having a diameter DS. If the cylinder over which the centers of the first spherical joints move is projected onto the plane PS in which the centers of the second spherical joints lie, an ellipse is obtained that has a major axis D/cos α and a minor axis D.
The machine further comprises a synchronization system for providing synchronization between the cylinder block 2 and the sliding disk 12. This synchronization is achieved by means of the coupling rods. More precisely, for each coupling rod, the synchronization system comprises a first drive surface formed on an extension 22A of a coupling rod 16 beyond the second spherical joint 16B and a second drive surface formed in a setback 22B into which said extension or lug 22A is engaged.
In general, for each coupling rod, the first drive surface is stationary relative to the coupling rod, while the second drive surface with which it co-operates is stationary relative to the sliding disk. Thus, the first and second coupling surfaces can, as in this example, be formed integrally respectively with a coupling rod and with the sliding disk, or else they can be secured to those parts.
As can be seen more clearly in
The tangential eccentricity is measured tangentially to the circle C described by the center CB of the second spherical joint while the sliding disk is rotating about the second axis of rotation AS.
The radial eccentricity eR is measured on a radius RA of the circle.
In
In
More precisely, the first drive surface 122A is formed by the circularly cylindrical surface of a segment 122A of the coupling rod that forms a lug, between the two spherical joints. The sliding disk has a central extension 13 which extends from the front face 12A of said disk towards the cylinder block 2. The central extension carries a plurality of hollow fingers 123, one for each coupling rod, each of said fingers providing a recess 122B through which the coupling rod passes.
Thus, in this example, the recesses are formed integrally with the sliding disk. However, it should be noted that the extension 13 could be a separate part mounted on and fastened to the disk.
The second embodiment is shown in the detail VII of
In
The slot 122B presents a plane of symmetry PY which is substantially parallel to a radius intersecting the second axis of rotation AS and which is offset relative to a radius RD of the sliding disk 12 passing through the center CB of the female portion 17A of the second spherical joint connecting the coupling rod under consideration to the sliding disk. The plan PY is offset relative to the axis AN of the female portion 17A of the spherical joint. As can be seen, said offset is such that the reference clearance between the lug 122A and the wall of the slot 122B which forms the second drive surface is small in the zone Z in which synchronization takes place while the cylinder block is rotating in the preferred direction R.
In this example, since the end-wall of the slot 122B is a cylinder portion, the center of curvature of said end-wall is represented by the axis AE, and radial eccentricity and tangential eccentricity that are indicated in
The variant in which the second drive surface is formed by a radial slot open on its side opposite from the second axis of rotation is usable in the second embodiment as shown, and also when, in general, the first drive surface is formed on a lug integral with or secured to a coupling rod engaged in said slot. The lug can be disposed between the spherical joints as in
Advantageously, each of the first and the second drive surfaces are defined at least in part by rotating a generator line about an axis. This applies, for example, for the end wall 123A of the slot 122B in
In
In a variant, at least one of the first and second drive surfaces has, in section perpendicular to the second axis of rotation AS, the shape of a curve whose curvature varies along the length of said curve. This applies, for example, for the second drive surface shown in
As indicated, the curve can also be modified so as to have at least one flat.
In
The invention applies to a motor or else to a pump having axial pistons, having a preferred rotation direction. The motor or the pump can have a single rotation direction, in particular if it is the pump of an open circuit or of a motor having a single rotation direction. It can also have a reverse rotation direction which is used exceptionally, e.g. when in a motor for driving a vehicle in translation, for reverse gear.
For example, for a machine having nine piston-and-cylinder assemblies distributed uniformly, and having a cubic capacity of 70 cm3, implemented in accordance with the first embodiment shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 0503345 | Apr 2005 | FR | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 3366968 | Iseman | Jan 1968 | A |
| 7013791 | Galba | Mar 2006 | B2 |
| Number | Date | Country |
|---|---|---|
| 21424 | May 1911 | GB |
| 522453 | Jun 1940 | GB |
| 1140167 | May 1967 | GB |
| WO2005078238 | Aug 2005 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 20060218786 A1 | Oct 2006 | US |
