WO2016097230A1

WO2016097230A1 - Integral roller piston and associated method

Info

Publication number: WO2016097230A1
Application number: PCT/EP2015/080375
Authority: WO
Inventors: Hervé Bernard DESUMEUR; Yann PRAT; Antoine Marc GALEA; Sébastien DAVID
Original assignee: Poclain Hydraulics Industrie
Priority date: 2014-12-17
Filing date: 2015-12-17
Publication date: 2016-06-23
Also published as: FR3030665B1; FR3030665A1

Abstract

The invention relates to a piston (1) with a roller (120) suitable for receiving a roller (120) and for sliding in a cylinder (2) along a sliding axis (C-C'), said piston (1) comprising a body (110) having a guide surface (111); an upper section (110a) having a cradle-shaped recess (112) suitable for receiving the roller (120); at least one centring element (130) for maintaining the centring of the roller (120) in the piston (1), and, further, the body (110), the at least one centring element (130) and the upper section (110a) comprising of a single piece integrally formed, and in that the opening angle (δ) of the cradle-shaped recess (112) is greater than 180°.

Description

Monobloc roller piston and method thereof

GENERAL TECHNICAL FIELD The invention relates to the field of pistons and in particular roller pistons.

In particular, the invention is advantageously used in hydraulic machines with radial pistons. STATE OF THE ART

A "piston with a roller" is a piston adapted to slide in a complementary chamber along a longitudinal axis and which carries at one of its ends a roller mounted to rotate about an axis transverse to the longitudinal axis and which rests on an associated room.

The roller pistons are used in particular in hydraulic devices. Some of these devices have a cylinder block comprising a plurality of radially distributed cylinders each comprising a roller piston resting on a lobed cam. The relative rotation of the cylinder block relative to the lobed cam induced by hydraulic pressure applied in the cylinders drives a shaft or vice versa, that is to say that the mechanically induced relative rotation generates a fluid pressure. Such devices are described, for example, in documents FR 2 651 836 and FR 2 955 903.

With reference to FIGS. 1a and 1b annexed, which respectively represent a assembled complete piston and the various parts composing a piston before assembly, a piston 1 generally comprises a body A110 comprising a cylindrical guide surface Al ll centered on a longitudinal axis of sliding CC . The body A110 seals in the associated cylinder 2, for example by means of an annular segment 151 engaged in a groove or complementary groove 150 at the base of the body A110 (Figure 2). The part upper Al lOa of the body has a shape of a cradle recess A112 for housing a roller 120 for rolling on a lobed cam 3. The pistons 1 follow the shape of the cam 3 during a relative displacement of rotation of the cylinder block relative to the cam 3 and thus move back and forth inside their cylinder 2 along the sliding axis CC.

Various technical additions have made it possible to make the piston 1 evolve. In order to allow the centering of the roller 120 in the piston, on the axis CC, the patent FR 2 561 836 proposes centering elements A130 placed on the lateral faces of the body A110. and orthogonal to the running axle RR 'of the rollers 120. These guide elements A130 accompany the piston 1 in its displacement along the sliding axis CC and prevent the translation of the roller 120 according to its rolling axis R-R'. Furthermore, according to one embodiment, a guide groove A131 provided on the outer surface of the centering elements A130 allows a clip (not shown) fixed in the cylinder block to engage in the guide groove A131 and thus to prevent the rotation of the piston along its axis of sliding C- C.

To maintain the roller 120 in position in the piston, the document FR 2 899 650 has a bearing A140 complementary shape to the cradle A112 of the piston 1 and which is housed at the bottom thereof. The pad A140 is made of one or more friction-limiting materials to promote rolling of the roller 120. The upper edges of the recess A112 and the pad A140 have stop or hold surfaces A113, A141, which consist of a deformation of the wall from the upper edges to the inside.

Currently, the realization of the cradle A112 is done by an additional machining operation in a direction transverse to the axis of the piston. But this technique combined with the necessary presence of A130 guide elements to position the roller involves a complexity and high manufacturing costs: elements requiring several machining, additional assemblies, robotic and manual deburring, etc.

The invention aims to overcome some of these problems while maintaining a strength and wear comparable to the prior art.

PRESENTATION OF THE INVENTION

For this, the invention has a roller bearing piston adapted to receive a roller and to slide in a cylinder along a sliding axis, said piston comprising:

a body having a guiding surface,

an upper portion having a recess in a cradle adapted to receive the rolling roller, the recess defining a bearing axis;

at least one centering element for maintaining the centering of the roller in the piston, and

in which the body, the at least one centering element and the upper part consist of a single piece made of material and in that the opening angle of the cradle recess is greater than 180 ° .

In addition, the centering element comprises an inner wall axially closing the cradle which extends relative to the rolling axis at an angle greater than or equal to 90 °, away from the recess, so as to "increase Its volume.

Such a piston represents a significant simplification of the processes. The opening greater than 180 ° and the fact that the centering element does not overhang the recess makes it possible to eliminate manufacturing steps, in particular to suppress the operation of transverse machining to realize the cradle (complex), and can be realized using a method using a single uniaxial compression step. The piston further comprises the following features, taken alone or in combination:

- The piston further comprises at least one arm, adapted to slide in the cylinder and prevent the rotation of the piston, wherein the arm has an inner wing located inside the notch of the recess and an outer wing located outside the piston body, the two wings being connected by connecting web astride the edge of the recess, the inner wing comprises attachment means in the form:

o a harpoon shape that locks in the notch of the recess, and / or

o a notch adapted to snap into a bore made on the piston body, at the notch, the outer flange comprises a catch and a spring is attached to the catch of the outer wing of the arm, the body comprises a peripheral groove adapted to receive a sealing ring and the diameter of the body between the upper part and the groove is greater than the diameter of the body on the other side of the groove, in order to avoid any contact of this region with the cylinder, the diameter of the piston is narrowed at the ends of the piston, that is to say at the top and at the other end, in order to optimize the pressure stresses in use, the piston is made by sintering the upper part has at least one boss, positioned at the top of the recess and oriented towards the inside of the recess. In addition, the invention also provides an assembly comprising a piston as described above, a roller and a bearing adapted to be fixed to the bottom of the recess and to be interposed between the bottom of the recess and said roller, said pad for facilitating the rolling of the roller in the recess.

The set may include the following features, taken alone or in combination:

the roller has an opening angle, that is to say the angle covered by the part of the roller which is in the open air, between 135 and

145 °,

the recess comprises at least one notch on its periphery and the pad has at least one tab of complementary shape to the notch of the recess, so as to block said pad in rotation,

- The recess has a blind hole and the pad comprises a stud complementary to said blind hole, adapted to be housed in said blind hole to limit movement of said pad

- The pad comprises at least one slot configured to come opposite the boss and allowing its introduction into the recess, the boss and the slot cooperating to facilitate the establishment and to maintain said pad in the recess.

The invention also proposes a hydraulic apparatus comprising a lobed cam and a cylinder block comprising a plurality of cylinders and a plurality of assemblies as previously described, each assembly being housed in a cylinder, the roller being able to come into contact with the cam lobed. In addition it is possible that each cylinder and each piston have complementary shape elements extending parallel to the sliding axis, one being recessed and the other projecting respectively on one of the piston or the piston. cylinder to prevent rotation of the piston in the cylinder during sliding of the piston along the axis of sliding.

Together with the invention, there is provided a method for manufacturing a piston for hydraulic machine with radial pistons, using a shaping apparatus comprising at least two elements movable in translation relative to one another. and a material, characterized in that it comprises the following steps:

- placing the material in the shaping equipment,

- Application by the apparatus of a uniaxial compression force along a compression axis,

no other force being exerted on the material, and one of the movable elements comprising a hemicylindrical projection directed along the axis of compression, for creating a semi-cylindrical recess in the material.

The method may include the following features, taken alone or in combination:

- for the process:

the apparatus comprises a matrix,

o the material is a metal powder,

the process comprises a step of heating the metal powder,

the process corresponding to a sintering,

- for the process:

the apparatus comprises a matrix and a pestle, where the material is a ferrous metal, the method comprises a step of heating the metal, the step of applying the compressive force being a fast striking, the method corresponding to a stamping, for the method:

the apparatus comprises a matrix and a counter-matrix, where the material is a non-ferrous metal,

the method comprises a step of heating the metal, the step of applying the compressive force being a slow compression and carried out using a hydraulic press,

the process corresponding to a stamping,

- The method comprises a machining step, - the method comprises a curing operation step,

- The method comprises a step of equipping the piston with a bearing and a roller, - the step of adding a pad is performed by spraying a coating on the recess,

- The method comprises a step of adding a roller, - the method comprises a prior step of cutting slots on two opposite faces of the pad, said slots being positioned to be opposite boss present in the top of the piston, - the stage the equipment of the pad comprises a step of embedding the pad in the recess, - The step of adding a pad in which the roller is inserted into a bearing by pressing and wherein the roller and the pad are then embedded in the piston 1, - the pad is held in place by a crimping step , thanks to a reserve of material present on the edges of the recess

- The hemicylindrical projection of the movable member comprises at least one recess at the corresponding portion at the top of the recess, so as to create a piston with boss.

PRESENTATION OF THE FIGURES Other characteristics, objects and advantages of the invention will emerge from the description which follows, which is purely illustrative and nonlimiting, and which should be read with reference to the appended drawings, in which:

FIGS. 1a and 1b show a piston according to the prior art respectively in the assembled position and in the exploded state before assembly,

FIG. 2 represents a piston known from the state of the art in its cylinder,

FIGS. 3a, 3b, 3b ', 3c, 3d represent different embodiments of the piston according to embodiments of the invention,

FIGS. 4a, 4b, 4c, 4d represent different embodiments of a pad according to the invention,

FIGS. 5a, 5b show an embodiment according to the invention comprising an arm,

FIG. 6 represents the angle of opening of the roller vis-à-vis the recess or a certain embodiment of the pad, FIG. 7 represents the general diagram of a device allowing a method of manufacturing the piston according to the invention,

FIGS. 8a, 8b, 8c show an embodiment of fixing of the pad according to the invention,

- Figures 9a and 9b show an embodiment of the recess and the pad.

DETAILED DESCRIPTION OF THE INVENTION

The piston 1

FIGS. 3a, 3b, 3c, 3d show various embodiments of the body 110 of a piston 1 according to the invention, some of which comprise, in assembled or exploded view, the roller 120 and the pad 140.

The body 110 comprises a guide surface 111, an upper portion 110a having a cradle recess 112, and a lower portion 110b, located opposite the upper portion 110a.

The guide surface 111 is cylindrical, centered on a longitudinal sliding axis C-C, preferably cylindrical in revolution about the axis C-C. It guides the piston 1 in a complementary cylinder 2 along the sliding axis C-C, as mentioned above.

The lower part of the body 110 may comprise, on a lower surface 190, a groove 191 preferably circular and centered with respect to the sliding axis C-C.

The cradle recess 112 is adapted to receive a roller 120. For this purpose preferably the recess 112 in the form of a cylindrical cavity of revolution about a bearing axis RR 'orthogonal to the longitudinal axis of sliding CC and secant of it. This cavity is open on the axial end of the body 110, that is to say that it does not cover 360 ° around the axis R-R ', but the recess 112 is not with convergent edges , that is to say, it covers an opening angular greater than 180 °. In other words, the recess in cradle 112 does not close on him. The roller 120 has a complementary outer diameter, with the required clearance, of the inside diameter of the cavity forming the recess 112. It is engaged in this cavity forming the recess 112 and rotates on itself along the bearing axis R -R. The body 110 further comprises at least one centering element 130 for maintaining the centering of the roller 120 in the piston 1, that is to say to prevent the roller 120 from protruding axially by translation along the rolling axis RR of the recess 112, on the cylindrical lateral surface of the body. The centering elements 130 are located in the upper part 110a, in two locations of the cradle recess 112 opposite diametrically with respect to the sliding axis CC, in order to prevent a translation of the roller according to the rolling axis R -R.

The centering element 130 comprises an inner wall axially closing the cradle 112. This wall is the one that acts as a stop for the roller 120. In order to allow the manufacture of the piston in a compression step, the inner wall extends relative to to the bearing axis RR 'at an angle greater than or equal to 90 °. The angle is measured between the part of the running axle RR 'situated in the recess 112 and the inner wall, in a plane of section through which the longitudinal cutting axis CC and the rolling axis R- R '. In other words, this means that the centering element 130, as it rises from the bottom of the recess 12, does not overhang said recess 112. Otherwise, the benefit of the upper opening at 180 ° for the recess 112 would be lost.

In one embodiment (FIG. 3a, 3c, 3d), each centering element 130 reaches the end of the upper part 110a of the body 110, that is to say that the cavity forming the recess 112 opens into a plane orthogonal to the sliding axis CC. In another embodiment (FIG. 3b), the cavity which forms the recess 112 is moreover itself open on its axial ends along the rolling axis R-R ', that is to say that it opens on the guide surface 111 of the body 110 in two diametrically opposite openings 132 on either side of the axis CC. The shape of these two openings 132 is circular and the center of the circle and put that that of the cradle recess 112, that is to say the rolling axis R-R '. The roller 120 then has on its axial ends along the rolling axis RR 'two cylindrical orifices 121, of cylindrical shape, positioned centrally on the circular ends (FIG. 3b'). The orifices 121 are adapted to roll on the openings 132 of the body 110.

The body 110, the upper part 110a, the at least one centering element 130 are according to the invention consist of a single piece of material. The outer surface of the centering elements 130 completes the cylindrical shape of the contact surface 110 to form a complete cylinder whose generatrices are parallel to the axis of sliding. Preferably, the assembly forms a cylinder of circular section.

Various manufacturing processes, in particular sintering, make it possible to obtain such parts and will be detailed later (see below). All processes have in common a step of striking the workpiece in one direction. This is the recess cradle 112 whose opening angle δ is greater than 180 ° which allows the use of such methods, when said recess is oriented in the direction of striking (along an axis similar to the sliding axis CC). This means that any section of the room is included in the previous when approaching the ends of the recess 112. Indeed, it would not be possible to demold the room if the recess was less than 180 °.

These processes reduce the manufacturing of parts and simplify the return and machining operations. In order to allow the rolling of the roller 120 in the cradle recess 112, a bearing 140 is disposed in said recess 112, between the piston 1 and the roller 120, thus limiting the friction.

The pad 140 may have convergent edges so that the opening angle δ 'of the roller 120 is less than 180 ° and is thus held in place in the recess (see below).

Several embodiments of the piston 1 will be described. These alternatives will not always be described for each of the embodiments, but those skilled in the art will be able to distinguish unambiguously the possible combinations.

Sealing The body 110 comprises a groove or peripheral annular groove 150, preferably located at the lower part 110b (see Figure 4a for example). The groove 150 is adapted to receive a seal or sealing ring (not shown and generally referred to as a "segment"), designed to slide on the inner surface of the associated cylinder and thus to isolate the cylinder 2 in two parts when the piston 1 is installed.

Narrowing Shape The body 110 of the piston 1 may have a constant diameter along its entire length along the axis of sliding C-C outside the cradle 112 and the groove 150 above (see figures).

It can also have a variable diameter. The diameter of the body 110 at the lower part 110b, typically below the peripheral groove 150, may thus be smaller than the diameter beyond the peripheral groove 150, that is to say towards the upper part 110a ( see Figure 4c for example). In this way, the body part 110 below the groove 150, more fragile, is not in contact with the cylinder 2.

This narrowing shape can be achieved by the previously mentioned methods (see above and infra).

Barrel shape

In addition, the shape of the body 110 of the piston 1 can also be narrowed at the axial ends along the sliding axis CC of the piston 1, in the upper part 110a and lower part 110b, in order to optimize the pressure stresses in use (no shown in the figures).

Embodiment of the recess with boss With reference to FIGS. 9a and 9b, this embodiment has an adaptation of the shape of the recess 112 and the pad 140. In the four angles formed by the recess 112 when reached the plane orthogonal to the sliding axis CC, the upper portion 110 has at least one boss 118 facing the interior of the recess 112. More concretely, the recess 112 has a hemicylindrical shape and over a certain axial length (along the axis R-R ') located near one end, the radius of the hemi-cylinder is lower so that a recess (the boss 118) extends from the upper portion 110a in the direction from inside the recess 112. Preferably, the radius of the hemicylinder gradually increases in the direction from the bottom to the top. In addition, it is important that the boss 118 does not project into a balcony above the recess 112, which would otherwise mean that the opening angle is not always greater than 180 °. Therefore, the boss 118 is not provided on the centering elements 130.

The reduction of this diameter is only carried out in the upper part of the recess 112, that is to say at the bottom of the recess, the radius is constant over the entire axial length of the recess 112 . Preferably, there are four bosses 118, each positioned near one of the four corners (see Figure 9b).

Complementarily, in order to be able to be put in place, the pad 140 has in proximity each corner, on two opposite sides, a partial cutout 144 forming a tongue, each cutout enabling the pad 140 to be placed at the level of the bosses (see FIG. 9a ). The cuts 144 are in the form of partial slots in the pad. These may be angled, extending towards the adjacent edge, for example, to better match the deformations due to the boss during installation.

Before placement, the pad 140 has a substantially rectangular shape. On each of two opposite faces, the two slots are made, extending towards the other opposite face. For reasons of symmetry, the two cuts 144 are each made at the same distance from the nearest respective edge.

The bosses 118 are developed before the introduction of the pad 140. Such an embodiment facilitates the deformation of the pad 140 during installation and avoids excessive deformation.

Embodiment of the blind hole recess

In this embodiment, shown in Figures 3a and 4a, the cradle recess 112 comprises a blind hole 160 which opens axially along the sliding axis CC on the body 110. The blind hole 160 is preferably cylindrical and circular. The cradle recess 112 then comprises the hemicylindrical cavity centered along the rolling axis RR 'and the blind hole 160. Additionally, the pad 140 comprises a stud 141, adapted to be housed inside the blind hole 160. plot 141 is of size and shape complementary to the blind hole 160. It can be achieved by crimping using a punch punch. Once installed, the pad 140 is thus locked in the cradle recess 112, which prevents it from being rotated by the roller 120 when it rolls on the cam 3. Any form of blind hole 160 and form complementary pad 141 for locking the pad 140 are suitable. We will favor the simplest realization.

In a particular embodiment, the pad 140 is formed of a semicylindrical shell of complementary shape to the cradle recess 112, and the pad 141 is a cylindrical tubular barrel projecting on the convex outer portion of said shell.

Preferably, the blind hole 160 and the stud 141 are located in the center of the piston 1 (on the sliding axis C-C) and the pad 140 respectively (see Figure 4a).

The blind hole 160 is particularly adapted to be achieved by the method of manufacturing the cradle recess. Indeed, it does not prevent demolding.

Embodiment of the tongue recess

In this embodiment shown in FIGS. 3c, 4b, 4c, the body 110 comprises at its wall which axially closes the cradle recess 112 at least one notch 115 at the periphery, according to the rolling axis RR '. preferably located along the axis of rotation RR 'of the roller 120. Preferably, a second notch 115 is located opposite the first notch 115. The two notches 115 are thus diametrically opposite to the sliding axis CC. Each notch 115 consists of an additional recess, whose depth is substantially equal to that of the maximum of the cradle recess 112. The pad 140 comprises a tongue 142 of complementary shape to each notch 115, adapted to fit into said notch 115 and prevent rotation of the pad 140. The tongue 142 is thus preferably centered on the hemispherical portion of the pad 140 (see Figure 4b ).

Conversely, an embodiment with the guide element 130 comprising a boss or gaudron located inside the recess 112 and a pad 140 having a notch is possible.

More generally, between the guide member 130 inside the recess and the pad 140, additional immobilization means can be provided.

In another form of the tongue-and-groove embodiment, shown in FIG. 4d, the body 110 comprises, at its wall which closes the cradle recess 112 orthogonal to the rolling axis R-R ', at least a notch 116 located at the top of the recess of the cradle 112, on its periphery.

Preferably, a second notch 116 is located opposite the first notch 116, symmetrically with respect to the sliding axis C-C. The notch 116 consists of a slight material withdrawal at the top 110a, where the recess meets the end of the piston 1.

The pad 140 comprises a tab 143 of shape complementary to the notch 116 adapted to fit into said notch 116 and to prevent rotation of the roller 120.

Therefore, the tab 143 is centered on the portion of the pad 140 located at the top of the recess 112 cradle.

In the same way, the notches 115, 116, as well as the boss, can advantageously be made by the same method as previously described. These do not prevent demolding.

Embodiment with the arm When the piston 1 comprises at least one notch 115 previously described, that is to say typically according to the axis of rolling R-R ', the piston 1 may comprise an arm 170, adapted to slide in the cylinder 2 and secured piston 1. This arm 170 prevents the rotation of the piston 1 in the cylinder 2 and can further maintain the pad 140 in place. For this, with reference to FIG. 5a, the arm 170 comprises an internal wing 171 located inside the notch 115 of the recess 112, and an outer wing 172 located outside the body 110 of the piston, on the guide surface 111 preferably. These two wings 171, 172 are interconnected by a connecting web 173 disposed astride the edge of the recess 112. The arm 170 has the general shape of an inverted "U". The two wings 171 and 172 are formed of elongated elements parallel to each other and which extend in a longitudinal direction parallel to the axis CC. They preferably have, at least for the outer wing 172, a constant section over their entire length.

Of a shape complementary to the outer flange 172, the cylinder 2 comprises a guide groove into which the outer flange 172 fits and in which the latter can slide to allow translation along the sliding axis C-C.

Preferably, the piston comprises two arms 170, arranged opposite one another, that is to say diametrically opposite to the sliding axis CC, and the cylinder 2 comprises two guide grooves complementary diametrically opposite with respect to the axis CC. The arms 170 and the pad 140 may be from the same piece of metal (folded sheet). In the embodiment with the arm 170, either the pad 140 has the tongue 142 to hold it in place, or the inner wing 171 of the arm 170 comprises fastening means 174 which allow maintain the pad 140 in place (Figure 5a, 5b), or both handsets (Figure 4c, 4d).

These attachment means 174 may take the form:

- A reference to the notch 115 of the harpoon type 174a which blocks the means 174 in place in the notch, not requiring any particular shape on the piston portion (not escaping the workpiece by simple buttressing), and /or

a notch 174b present on the inner wing 171 which is deflected in the direction of the outer wing; this notch 174b which cooperates with a bore 174c in the piston 1. The piercing 174c is made by drilling through. This is the only transverse machining recovery step for the piston 1. The elasticity of the notch 174b allows clipping and holding the arm 170 in place. Clipping is then performed by a hand press.

The pad 140 may be flexible. In this way, if the pad 140 closes on itself, so that the opening angle of the roller δ 'is less than 180 °, the roller 120 is held in place.

Independently, the arm 170 may comprise a hook 175 on the outer wing 172. Indeed, in the case of retractable radial piston hydraulic machine, to allow a freewheel mode, the pistons 1 comprise a spring 180 (see Figure 5b in particular) which allows to keep them inside their respective cylinder 2, without contact with the cam 3. The presence of a spring 180 is not limited to the embodiment with the arm 170 (see Figure 2 for example, where the spring 180 is attached to the lower base of the piston 1 through the groove 191 which can accommodate).

In the present case (FIG. 5b), the spring 180 can be hooked to the catch 175. Preferably, there is a catch 175 on each arm 170.

The hook 175 may be subject to different embodiments. It may be for example a projection or hook placed on the end of the outer flange 171 of the arm 170, opposite to the connecting core 173. Embodiment without the arm

In order to prevent rotation of the piston 1 in the cylinder 2, the piston 1 (which then has no arms 170), may comprise a guide groove on the guide surface 111 (similarly to the guide groove 131 of the piston of Figure 2 but not shown in the following figures). This groove has a direction parallel to the sliding axis C-C. In a complementary manner, the inner wall of the cylinder 2 comprises a projecting, fixed element able to slide in said groove 131. This is an inversion with respect to the embodiment with the arm 170.

Generally, the piston 1 and the cylinder 2 have complementary shape elements groove / rib or tenon / mortise extending parallel to the sliding axis CC, one being recessed and the other protruding respectively on one of the piston 1 or the cylinder 2. Shape of the pad 140

Depending on the hydraulic machines used, the roller 120 is always held in contact with the cam 3 or it is sometimes distant. In the first case, the roller 120 is held in the recess 112 through contact with the lobed cam 3 and therefore does not need to be trapped in the shape of the upper part 110a or the pad 140. Therefore, in this case there is no particular constraint of opening angle δ 'of the roller 120, which may be greater than 180 °, as is the opening angle δ of the recess 112. In this case the pad 140 preferably do not have convergent edges. The opening angle of the roller δ '(see FIG. 6) corresponds to the angle defined by the straight lines passing through the center of the recess 112 or the center C of the roller 120 (located on the axis of rotation R-R ', the two definitions being equivalent) and the ends of the recess 112 and / or the pad 140. It is therefore the angle in which the roller 120 is "free" or in other words the angle by which the cradle is open, ie by which the roller emerges and is accessible outside the recess 112 and / or the pad 140. When it is calculated with the edges of the recess 112, it is equal to the opening angle δ of the recess 112. This is a special case. In other words, in a sectional plane transverse to the rolling axis R-R ', it is defined by the angle between the two straight lines passing through the rolling axis RR' and respectively the two ends of the recess in cradle 112.

In the second case (roller 120 away from the cam 3), it is however necessary that the opening angle δ 'of the roller 120 is strictly less than 180 °. The angle range is defined by the values 130 ° and 150 °, with a value preferably between 135 and 145 °. In this case the pad 140 has convergent edges. The more the angle δ 'is close to 180 °, the more the assembly of the piston 1, the pad 140 and the roller 120 is easy. On the other hand, the roller 120 is held more precariously inside the recess 112.

When the angle is less than 130 °, the roller 120 is reliably maintained but there is a risk of contact between the pad 140 and / or the upper portion 110a and / or the pad 140 with the cam 3. On the other hand it becomes more difficult to assemble the elements: the diameter of the roller 120 becomes much greater than the available space at the ends of the pad 140. The insertion is performed in different ways that will be explained in the process part. The piston 1 may also comprise a friction pad (not shown in the figures) situated between the roller 120 and each centering element 130 in order to limit the friction between the roller 120 which rotates along the bearing axis RR 'and the centering element 130 fixed in the reference frame of the piston 1.

Manufacturing process

For the manufacture of a piston 1 whose elements came from material, as explained above, several embodiments are possible. In particular, the body 110 whose guide surface 111, the at least one guide surface 113 are made of material.

To do this, the method P uses a material P10 and a shaping apparatus P20. Figure 7 (sectional view defined by the plane comprising the axes of rotation R-R 'and compression K-K') illustrates the general principle and will be used to illustrate the various embodiments. The methods have in common to comprise a compression step along a single axis K-K ', which is collinear with the sliding axis C-C, so that the recess cradle 112 open at least 180 ° can be realized.

The shaping apparatus P20 comprises several axial compression tools P21, P22 movable in translation relative to each other, which may each comprise different shapes for molding the elements mentioned above, such as the blind hole 160 , the notches 115, 116.

In the embodiment of Figure 7, we can see:

on the compression tool P22, a cylindrical projection P221 making it possible to make the blind hole 160, a flat part P222 making it possible to make the notch 116, and the semi-cylinder P223 making it possible to make the recess in the cradle 112,

on the compression tool P21, a projecting ring P211 making it possible to prepare the annular groove 150, a protrusion circular P212 to make the groove 191 to accommodate the spring 180.

Other elements do not appear in FIG. 7 (out-of-plane): there may be mentioned, if the tool P22, at least one axial projection, making it possible to make the notch 115. On the contrary, it may be an axial projection on the tool P21 to make the boss (see below) to immobilize the pad 140.

In addition, the shaping apparatus P20, in particular the hemicylindrical projection P223 of the movable member may be adapted to manufacture a piston having the bosses 118 presented above, in particular by using recesses. These bosses 118 may be made before the installation of the pad. They can be sized to allow insertion of the pad. When the pad 140 is inserted, it will pass between the bosses 118 by deforming by elastic flexion. The pad 140 will then spread and will remain trapped in the cradle 112 because of the bosses 118 and the piston.

Only the shapes perpendicular to the compression axis K-K '(thus to the sliding axis C-C) can not be performed. This is why the piston described above essentially has characteristics not perpendicular to the compression axis K-K '(such as a recess 112 with an opening angle δ of greater than 180 °).

Embodiment by sintering

The material P10 is a metal powder and the shaping apparatus P20 comprises a matrix.

The metal powder P10 is inserted into the matrix P20, which comprises a unixial compression tool P21, P22, and the metal powder P10 is compressed by compression in a single direction. To do this, the matrix P20 comprises a chamber of constant section in which the powder P10 is inserted and the compression tool comprises a piston P22 of complementary section of the chamber moved to translation into the chamber after insertion of the powder against an abutment P21 closing the opposite end of the chamber, or two pistons P21 and P22 complementary section of the chamber moved in opposite directions towards the center of the chamber to compress the powder P10 .

The agglomerate then obtained is taken out and then heated to cohere the particles.

This process corresponds to sintering.

It is understood that all the aforementioned elements (blind hole 160, notch 115, 116, recess cradle 112, groove 180) can be made by this method.

One of the advantages of such a process is the porosity of the material, which allows a lubricant to be inserted and thus makes self-lubricating bearings.

In one embodiment, the pad is clipped with the catch of attachment means 174.

Embodiment Embossing The material P10 is a metal in the form of a blank, preferably ferrous, and the forming apparatus P20 comprises a matrix P21 and a pestle P22.

The blank is inserted into the matrix P20 and the pestle P22 strikes the blank in a single direction to deform it. The excess of the blank, called burr, can join a burr slot provided in the die.

The blank may be preheated before being inserted into the die, thereby facilitating deformation.

This process corresponds to stamping.

A machining step is then performed, in particular to remove the burr.

Embossing embodiment The material P10 is a metal in the form of a blank, preferably non-ferrous, and the shaping apparatus P20 comprises a matrix P21 and a contravener P22.

This process corresponds to a stamping.

The blank is inserted into the die P21 and the contravener P22 slowly compresses the blank in one direction, using a hydraulic pressure. Embodiment by injection molding (MI M - metal injection molding)

The material P10 is a metal powder to which a binder has been added and the shaping apparatus P20 is a matrix.

The powder P10 with the binder is injected and then decanted in an oven under a controlled atmosphere. The part is then sintered at a temperature above 1000 ° C.

Additional steps

Following the first step of manufacturing the raw piston, it is necessary to machine some elements.

In particular, the guide surfaces 111, which rub against the cylinder 2, must be machined and ground, to ensure good accuracy of the part.

This machining allows in particular to shrink the ends of the piston as it has been mentioned (see above).

The annular peripheral groove 150 can also be machined in this way. Curing steps obtained by heat treatment or including a heat treatment step are performed. Then, the sealing segment 151 is laid. Alternatively, the sealing segment 151 can be placed after the pad 140 or the pad 140 and the roller 120.

These two steps are performed indifferently.

The pad and the roller

Once the piston 1 is ready, the pad 140 must be added.

There are several embodiments for this purpose.

The pad 140 may be formed by spraying a plastic resin type coating on a few tenths of a thickness on the surface of the recess 112. It can also be formed by a so-called additive manufacturing technique, by adding friction material ( regulates or bronze)

Alternatively, the pad 140 may be rigid and shaped to fit the recess 112.

Alternatively, the pad 140 may be flexible to be inserted into the recess 112.

In the embodiment with the arm 170, the pad 140 and the arm 170 are pressed into the recess 112 and lock with the means 174.

Depending on the type of pad 140 used, the opening angle of the roller δ 'may be less than 180 °.

In the case of an opening angle δ 'of at least 180 for the roller 120, the roller 120 is put in place after the installation of the pad 140.

Conversely, in the case of a roller 120 held in place by the pad 140, the roller 120 is placed in the pad 140 before pressing ("press fit" in English) and then both are embedded in the recess 112 of the piston 1.

The piston 1 may comprise material reserves 117 at the edge of the recess 112 (FIG. 8a). In this way, when the pad 140 is placed (FIG. 8b), crimping can be performed at using a punch on each stock of material, which is deformed to cover the end of the pad 140 and block it in the recess 112 (Figure 8c). This technique is advantageous for a rigid pad 140. It makes it possible to obtain a piston 1 assembled, that is to say comprising the segment and the pad that do not disassemble. Such a piston is then ready for use.

Once the pad is installed, the roller 120 is placed in the recess 112. For the roller to be inserted, the opening angle of the recess 112 must be at least temporarily greater than 180 °.

Subsequently, and according to the desired embodiments of the piston, the pad 140 is folded slightly above the roller 120 to reduce the opening angle to the desired values, for example to form a housing with convergent edges adapted to maintain the stone

120 in place on the piston 1 (in the case where the roller 120 does not remain in contact with the cam 3).

Summarized (not limiting), there is the step of producing the piston 1 by uniaxial compression, then a machining step, a hardening step and a step of laying the pad 140 with the roller 120 as well as segment 151 just before or after.

These steps make it possible to obtain a piston 1 equipped and ready to use.

Claims

claims

Piston (1) with a roller (120) adapted to receive a roller (120) and to slide in a cylinder (2) along a sliding axis (C-C), said piston (1) comprising:

a body (110) having a guiding surface (111),

an upper portion (110a), having a cradle recess (112), along an axis of rolling (R-R '), adapted to receive the roller (120),

at least one centering element (130) configured to maintain the axial centering of the roller (120) in the piston

(1) along the rolling axis (R-R '), and

the piston (1) being characterized in that the body (110), the at least one centering element (130) and the upper part (110a) consist of one and the same piece of material and in that the opening angle (δ) of the cradle recess (112) is greater than 180 °, the opening angle (δ) being defined by the passing angle, in a transverse cutting plane at the running axle (R-R '), by the bearing axis (R-R') and two ends of the recess (112), the angle being that for which the cradle recess (112) is open , and wherein the centering element (130) comprises an axially axially closing inner wall (112), said wall extending with respect to the rolling axis (R-R ') at an angle greater than or equal to 90 °, away from the recess (112).

Piston (1) according to claim 1, further comprising at least one arm (170), adapted to slide in the cylinder (2) and prevent the rotation of the piston (1), wherein the arm (170) has an internal wing (171) located inside a notch (115) of the recess (112) and an outer wing (172) located outside the body (110) of the piston (1), the two wings (171). , 172) being connected by link core (173) astride the edge of the recess (112).

3. Piston (1) according to claim 2, wherein the inner wing comprises fastening means (174) in the form:

a harpoon shape (174a) which locks in the notch (115) of the recess (112), and / or

- A notch (174b) adapted to snap into a bore made on the body (110) of the piston (1), at the notch (115).

4. Piston (1) according to claim 3, wherein the outer flange comprises a catch (175) and a spring (180) is fixed to the catch (175) of the outer flange of the arm (172).

The piston (1) according to one of claims 1 to 4, wherein the body (110) comprises a circumferential groove (150) adapted to receive a sealing ring and the diameter of the body (110) between the upper portion (110a) and the groove (150) is greater than the diameter of the body (110) on the other side of the groove (150) to prevent contact of this region with the cylinder (2).

6. Piston (1) according to any one of claims 1 to 5, wherein the diameter of the piston (1) is narrowed at the ends of the piston (1), that is to say at the top and the bottom. other end, in order to optimize the pressure stresses in use.

7. Piston (1) according to any one of claims 1 to 6, characterized in that it is produced by sintering.

8. Piston (1) according to any one of claims 1 to 7, wherein the upper portion (110a) has at least one boss (118), positioned at the top of the recess (112) and oriented toward the interior of the recess (112).

9. An assembly comprising a piston (1) according to any one of claims 1 to 8, a roller (120) and a bearing

(140) adapted to be fixed to the bottom of the recess (112) and to be interposed between the bottom of the recess (112) and said roller (120), said pad (140) facilitating the rolling of the roller ( 120) in the recess (140).

10. The assembly of claim 9, wherein the roller (120) has an opening angle (δ '), that is to say the angle covered by the part of the roller (120) which is at the free air, between 135 and 145 °.

11. Assembly according to one of claims 9 or 10, wherein the recess comprises at least one notch (115, 116) on its periphery and the pad (140) has at least one tongue (142, 143) of complementary shape at the notch (115, 116) of the recess (112), so as to lock said pad (140) in rotation.

12. An assembly according to one of claims 9 to 10 wherein the recess (112) has a blind hole (160) and the pad (140) comprises a stud (141) of complementary shape to said blind hole (160) adapted for housing in said blind hole (160) to limit movement of said pad (140).

An assembly according to any one of claims 9 to 12, in combination with claim 8, wherein the pad

(140) comprises at least one slot (144) configured to face the boss (118) and allowing it to be inserted into the recess (112), the boss (118) and the cooperating slot (114) to facilitate placement and to maintain said pad (140) in the recess (112).

A hydraulic apparatus comprising a lobed cam (3) and a cylinder block comprising a plurality of cylinders (2) and a plurality of assemblies according to any one of claims 9 to 13, each assembly being housed in a cylinder (2). ), the roller (120) can come into contact with the lobed cam (3). Hydraulic apparatus according to claim 14, wherein each cylinder (2) and each piston (1) have complementary shape elements extending parallel to the sliding axis (CC), one being recessed and the other protruding respectively on one of the piston (1) or the cylinder (2) to prevent rotation of the piston (1) in the cylinder (2) during sliding of the piston (1) along the axis of sliding .

16. A method of manufacturing a piston (1) according to claim 1, using a shaping apparatus (P20) comprising at least two elements movable in translation relative to each other ( P21, P22) and a material (P10), characterized in that it comprises the following steps:

- placing the material in the shaping equipment,

- application by the apparatus of a uniaxial compression force along a compression axis (Κ-Κ '),

no other force being exerted on the material, and one of the movable elements (P22) comprising a semicylindrical projection (P223) directed along the axis of compression (Κ-Κ '), making it possible to create a semi-cylindrical recess (112 ) in the material (P10).

The method of claim 16, wherein:

the apparatus (P20) comprises a matrix (P21),

the material (P10) is a metal powder, the process comprises a step of heating the metal powder,

the process corresponding to sintering. 18. The method of claim 16, wherein:

the apparatus (P20) comprises a matrix (P21) and a pestle (P22),

the material (P10) is a ferrous metal,

the process comprises a step of heating the metal,

the step of applying the compressive force being a rapid strike,

the method corresponding to a stamping.

The method of claim 16, wherein:

the apparatus (P20) comprises a matrix (P21) and a counter-matrix (P22),

the material (P10) is a non-ferrous metal,

the process comprises a step of heating the metal,

the step of applying the compressive force being a slow compression and performed using a hydraulic press, the method corresponding to a stamping.

20. Process according to any one of claims 16 to 19, comprising a machining step.

21. A method according to any one of claims 16 to 20, comprising a hardening step.

22. A method according to any one of claims 16 to 21, comprising a step of equipping the piston (1) with a pad (120) and a roller (120).

The method of any one of claims 16 to 22, wherein the step of adding a pad (140) is performed by spraying a coating on the recess (112). 24. The method of claim 23, comprising a step of adding a roller (140).

25. The method of claim 22, comprising a prior step of cutting slots (144) on two opposite faces of the pad (140), said slots (140) being positioned to be facing boss (118) present in the top ( 110a) of the piston (110).

26. The method of claim 25, wherein the step of equipping the pad comprises a step of embedding the pad in the recess.

A method according to any one of claims 16 to 22, wherein the roller (120) is inserted into a bearing (140) by pressing and wherein the roller (120) and the bearing (140) are then embedded in the piston 1.

28. A method according to any one of claims 16 to 25, wherein the pad (120) is held in place by a crimping step, thanks to a material reserve (171) present on the edges of the recess (112). ).

The method of any one of claims 16 to 28, wherein the hemicylindrical projection (P223) of the movable member (P22) comprises at least one recess at the corresponding portion at the top of the recess (112). , so as to create a piston according to claim 8.