WO2014174166A1

WO2014174166A1 - Ball-ended piston/connecting-rod assembly

Info

Publication number: WO2014174166A1
Application number: PCT/FR2014/050641
Authority: WO
Inventors: Benjamin Petit; Mehdi El Fassi
Original assignee: Peugeot Citroen Automobiles Sa
Priority date: 2013-04-24
Filing date: 2014-03-19
Publication date: 2014-10-30
Also published as: FR3005132B1; EP2989353A1; FR3005132A1

Abstract

The invention relates to an assembly (1) comprising a piston (2) having a central axis (Z), a connecting rod (3), the piston (2) being articulated to the connecting rod (3) by a ball joint between a spherical surface (S1) belonging to the piston and a spherical surface (S2) belonging to the connecting rod (3), means of supplying a lubricant under pressure so that it infiltrates between the two surfaces (S1, S2), characterized in that the ball joint comprises, on one of the spherical surfaces (S1, S2), lubricant guide means configured in such a way that the lubricant forced to circulate therein through viscous friction causes the piston (2) to rotate about the central axis (Z) thereof.

Description

PISTON-ROD ASSEMBLY

Technical field of the invention

The present invention relates to the field of piston machines. The invention relates more particularly to piston-connecting rod assemblies whose piston is hinged to the connecting rod by a ball joint.

Technological background

The operating cycle of a four-stroke piston engine is analytically decomposed into four stages or phases: intake, compression, (combustion) expansion, exhaust. The movement of the piston is initiated by the combustion of a mixture of fuel and air that takes place during this cycle.

The piston moves during start-up through an external power source, often through a starter, until at least one combustion and trigger produces a force capable of providing the other three times . The motor then works alone and produces a torque on its output shaft.

In order to reduce consumption and therefore polluting emissions, without compromising power, it is known to reduce the engine displacement while increasing the power delivered by each cylinder. However, such an increase in power leads to an increase in the pressures in the cylinders, which induces mechanical resistance problems and frictional motor loss increase, also referred to as PMF.

With the piston sliding in a jacket, the Segment - Piston - Jacket zone represents a high share of friction motor losses. Indeed, the establishment of a zero velocity at Top Dead Point (TDC) and Low Dead Point (TDC) during the conventional operation of a four-stroke engine implies limiting lubrication regimes with a high metal-to-metal friction because the surfaces are no longer separated by the oil, and therefore a strong increase of the PMF at these two stages.

Document GB2361517 discloses an assembly comprising a piston and a connecting rod, the articulation between the piston and the connecting rod being ensured by a ball joint connection. Such articulation allows the rotation of the piston about its axis. A central channel in the body of the connecting rod brings the lubricating oil to the ball joint. However this arrangement does not allow to control the lubrication regime for maintaining a lubricant film in particular at Top Dead Point and Low Dead Point.

Document US1904126 discloses an assembly comprising a piston and a connecting rod, the articulation between the piston and the connecting rod being ensured by a ball joint connection. Such articulation allows the rotation of the piston about its axis. In this assembly, the piston is forced in rotation to uniformize the wear of the skirt, the rotational force being created by the thrust of the combustion gases on a suitable shape of the piston head. However, this arrangement does not allow more to control the lubrication regime for maintaining a lubricant film in particular at Top Dead Point and Low Dead Point.

Therefore, the problem underlying the invention is to control the lubrication regime of the joint connecting the piston and the connecting rod of a piston-rod assembly.

An object of the present invention is to provide an assembly comprising a piston and a connecting rod connected by a hinge whose structure allows a control of the lubrication regime of the joint and the maintenance of a lubricant film in particular at the passage of the Dead Center High and Low Dead Point.

To achieve this objective, an assembly is provided according to the invention comprising a piston having a central axis, a connecting rod, the piston being articulated on the connecting rod by a ball joint connection between a spherical surface belonging to the piston and a spherical surface belonging to the connecting rod means for supplying a lubricant under pressure so that it is inserted between the two surfaces, the ball joint comprising on one of the spherical surfaces lubricant guiding means arranged so that the lubricant brought to circulate therein. Viscous friction causes the piston to rotate about its central axis.

Preferably, the guide means comprise a groove.

Preferably, the guide means have an arc shape.

More preferably, the guide means have a spiral shape.

In a variant, the guiding means extend from an outlet orifice of the lubricant supply means. In another variant, the rod is held in translation relative to the piston by means of a closure cup attached to the piston.

In another variant, the connecting rod comprises a spherical end for the ball joint, the spherical end being removable.

Preferably, the spherical tip comprises a lubrication port of the contact interface with the closure cup.

In a variant, the piston comprises segments each comprising an opening, the segments being locked in rotation in a position where the openings are not facing each other.

The invention also relates to a piston machine comprising an assembly according to any one of the previously described variants.

Preferably, the piston machine is an internal combustion engine.

Brief description of the drawings

Other features and advantages will appear on reading the following description of a particular embodiment, not limiting of the invention, with reference to the figures in which:

- Figure 1 is an axial sectional view of a piston-rod assembly of the invention.

- Figure 2 is a perspective view, with the piston in section of the connection between the piston and the connecting rod.

- Figure 3 is a perspective view of a spherical tip comprising a lubricant guide groove arranged on the surface of the sphere.

- Figure 4 is a perspective view of a variant for which the lubricant guide groove is formed in the spherical surface of the piston.

- Figure 5 is a perspective view of a spherical tip comprising a lubrication groove of the contact interface between the spherical tip and the closure cup.

FIG. 6 is a diagram detailing the physical principle of the invention. detailed description

Figure 1 shows an axial section of an embodiment of a rod-piston assembly of the invention. This rod-piston assembly is intended to equip preferably a piston 4 thermal engine. In Figure 1 the assembly 1 comprises a piston 2 and a connecting rod 3. In Figure 1, the piston 2 extends cylindrically along a central axis Z. The seal between the piston 2 and the sleeve 23 of the piston engine alternative is provided classically by sealing segments 22.

The piston 2 is articulated on the rod 3 by a ball joint connection between a spherical surface S1 belonging to the piston and a spherical surface S2 belonging to the connecting rod 3.

The connecting rod 3 comprises three parts:

a soul 5 which forms its central part,

a connecting rod cap 6 intended to be fixed on the core 5 and which delimits therewith a circular bore 7. This part is conventionally called a small end, a spherical end 8 forming the small end.

In Figure 1, the piston 2 and the rod 3 are aligned along the Z axis. This arrangement is found when the assembly 1 is used on a piston engine and correspond to the passage of the Top Dead Center and the Low Dead Point.

The rod 3 furthermore comprises an internal pipe 9 extending from an inlet orifice 10 at the level of the circular bore 7 to an outlet orifice 1 1 (see FIG. 2) at the level of the spherical tip 8. , passing through the core 5 of the rod and the spherical end 8. This conduit 9 has the function of bringing a lubricant, such as oil under pressure to the ball joint.

In operation, the lubricating oil enters through the inlet orifice 10 at the level of the circular bore, through the inner pipe 9 and opens at the ball joint connection through the outlet orifice 1 1 to come s' interposing between the two surfaces S1, S2, forming an oil film and reducing the friction between the two surfaces S1, S2. The piston 2 may comprise a volume 20, such as a spherical cap, set back from the spherical surface S1 and making it possible to make an oil reserve.

In this embodiment, the spherical tip 8 is a removable piece which comprises a gripping zone 12 surmounted by a sphere 13 for the ball joint connection. For the sake of simplicity, the spherical tip 8 can be assembled on the core 5 of the connecting rod by screwing the nozzle 8 directly on the core 5 of the connecting rod. In this case, it is provided on the gripping zone 12 flats 14 which allow the use of a tool for gripping the tip 8 and its screwing on the core 5 of the rod 3.

In Figure 1 or Figure 2, the rod 3 is held in translation relative to the piston 2 by means of a closure cup 15 fixed to the piston. In Figure 1, the closure cup 15 is held by two screws 16, 16 'fixing.

In this embodiment the ball joint comprises a groove 17 extending from the spiral-shaped exit orifice 1 1 on the spherical surface S 2 belonging to the connecting rod 3. According to the invention, this groove 17 in Spiral shape forms lubricant guide means. The displacement of the lubricant circulated in the groove 17 causes, by viscous friction on the surface S1, the piston 2 rotated about its central axis Z. This forced rotation of the piston 2 allows to always have a differential speed between the two surfaces S1, S2 and avoid passing through a zero differential speed and a limit lubrication regime with contact friction between the two surfaces. A groove has the advantage of being easy to produce, for example by machining. The spiral has the advantage of precisely guiding the lubricant over a long distance

Figure 6 shows another example in which the lubricant guiding means has an arcuate shape 21 extending from the outlet port 1 1. In this other example, the arc makes the lubricant follow a determined path. Along this path, the lubricant punctually has a vector velocity V. This vector which can be decomposed in a plane perpendicular to the central axis Z according to a radial component Vn and a tangential component Vt. This tangential component Vt generates a viscous friction which causes the piston to rotate about its central axis Z. The same principle applies to the spiral.

Other forms may be suitable, the essential thing is that the lubricant guiding means make the lubricant follow a path which causes the lubricant to have a speed component allowing the piston to be rotated about its central axis Z, when the piston is at the top dead center or low dead point, by viscous friction generated by this speed component.

FIG. 3 shows a variant in which the spherical tip 8 comprises an additional oil outlet orifice 18 at the interface 19 (see FIG. closure cup 15 and the sphere 13 to improve the lubrication of this interface 19.

FIG. 4 shows a variant in which the groove 17 is arranged on the spherical surface S1 of the piston 2. In this variant, the spiral-shaped groove 17 acts as a means of guiding the lubricant arranged so that the lubricant supplied to the piston circulating leads by viscous friction the piston 2 in rotation about its central axis Z (Figure 1). The spiral extending from a point 22 which is substantially in front of the outlet orifice 1 1 of the lubricant supply means, when the piston and the connecting rod are aligned (Figure 1).

FIG. 5 shows a variant in which an additional groove 17 'is arranged on the spherical surface S2 of the spherical tip 8 at the interface 19 (see FIG. 2) of contact between the closure cup 15 and the sphere 13 to improve the lubrication of this interface 19. The groove 17 'is shown spirally, but the effect sought in this case is the lubrication and not the rotation of the piston.

In the embodiments described, the spherical surface S1 of the piston 2 constitutes the female part of the ball joint while the surface S2 of the spherical end constitutes the male part of the ball joint. In a variant not shown, the reverse can be provided, ie a spherical surface S1 of the piston 2 constituting the male part of the ball joint and a spherical surface S2 of the spherical tip 8 constituting the female part of the ball joint. In this case, the ball joint may equally well comprise, on one of the spherical surfaces S1, S2, lubricant guiding means as described above.

In another variant not shown, the guide means may be formed by a series of cells arranged on one of the surfaces forming a suitable path for the lubricant, for example in the form of an arc or a spiral.

The seal between the piston 2 and the liner 23 of the reciprocating piston engine is conventionally provided by sealing segments 22. These segments each include an opening to be arranged on the piston. The rotation of the piston can cause these segments to rotate. The rotation of these segments will pass through a phase during which the openings of the segments will be face to face and thus let the oil present on the jacket and / or the gases contained in the cylinder. It is thus possible to provide sealing segments locked in rotation in a so-called sealed position, that is to say in a position where the openings are not facing each other. The locking in rotation of each segment can be achieved by a stop pin.

This rotation of the piston takes place during the entire operating cycle of the engine and more particularly at top dead center and bottom dead center. The expected order of magnitude of the rotational speed of the piston is between 10 and 50 rpm for an oil pressure of about 4 bar.

Compared to a conventional connection of the piston-rod type per axis, the use of a piston-rod-type connection by ball joint makes it possible to increase the area available for transferring the pressure force from the piston to the connecting rod and thus to tolerate higher load levels. The invention also makes it possible to reduce engine friction losses on an engine cycle by promoting the establishment of a lubrication regime that keeps the lubricant film throughout the operating cycle.

In the case of an internal combustion engine, the invention makes it possible to reduce frictional motor losses, which results in a reduction in carbon dioxide emissions.

The piston-rod assembly of the invention can equip piston machines other than an internal combustion engine.

Claims

claims

1. Assembly (1) comprising a piston (2) having a central axis (Z), a connecting rod (3), the piston (2) being articulated on the connecting rod (3) by a ball joint connection between a spherical surface (S1) belonging to the piston and a spherical surface (S2) belonging to the connecting rod (3), means for supplying a lubricant under pressure so that it can be inserted between the two surfaces (S1, S2), characterized in that the connection ball comprises on one of the spherical surfaces (S1, S2) lubrication guide means arranged so that the lubricant brought to circulate there at a speed (V) which is decomposed in a plane perpendicular to the central axis (Z) according to a radial component (Vn) and a tangential component (Vt), the tangential component (Vt) generating a viscous friction which causes the piston (2) to rotate about its central axis (Z).

2. An assembly according to claim 1, characterized in that the guide means comprise a groove (17).

3. An assembly according to claim 1 or claim 2, characterized in that the guide means have an arcuate shape (21).

4. Assembly according to any one of the preceding claims, characterized in that the guide means have a spiral shape.

5. An assembly according to any one of the preceding claims, characterized in that the guide means extend from an orifice (1 1) output lubricant supply means.

6. An assembly according to any one of the preceding claims, characterized in that the connecting rod (3) is held in translation relative to the piston (2) by means of a closure cup (15) fixed to the piston (2). ).

7. An assembly according to any one of the preceding claims, characterized in that the rod (3) comprises a spherical tip (8) for the ball joint, the spherical tip (8) being removable.

8. The assembly of claim 7 with claim 6, characterized in that the spherical tip (8) comprises a lubrication port of the interface (19) of contact with the closure cup (15).

9. An assembly according to any preceding claim characterized in that the piston (2) comprises segments (22) each comprising an opening, the segments being locked in rotation in a position where the openings are not facing each other.

Piston machine comprising an assembly according to any one of the preceding claims.

1 1. Piston machine according to claim 10, characterized in that it is an internal combustion engine.