FR3087235A1 - BALANCED ROTARY SHAFT, ESPECIALLY A CRANKSHAFT, PARTIALLY CARRIED OUT BY AN ADDITIVE MANUFACTURING TECHNIQUE, MANUFACTURING METHOD AND MOTOR EQUIPPED WITH SUCH A SHAFT - Google Patents

Abstract

The invention provides a crankshaft (100) comprising a main body (101) which comprises at least two journals (105) for guiding the crankshaft in rotation (100) and at least one balancing counterweight (106), in which the counterweight (106) comprises a central part (PCR) for connection to at least one guide pin (105), and a main part (PPC) forming a counterweight which is connected to the central part (PCR) for connection and which is offset radially by relative to the axis (A) of rotation of the rotary shaft (100), characterized in that at least a portion (200) of at least one part (PCR) of the counterweight (106) is produced by a manufacturing technique additive, for example by laser deposition.

Description

Balanced rotary shaft, in particular engine crankshaft, produced in part by an additive manufacturing technique, manufacturing process and engine equipped with such a shaft

TECHNICAL FIELD OF THE INVENTION

The invention relates to the design of a balanced rotary shaft such as a crankshaft, in particular of the engine of a motor vehicle.

TECHNICAL BACKGROUND OF THE INVENTION

The invention relates more particularly to a rotary shaft, and in particular a crankshaft of a multi-cylinder internal combustion engine intended in particular to equip a motor vehicle.

The invention more particularly aims to improve the balancing of a crankshaft.

The crankshaft or drive shaft of a multi-cylinder combustion engine receives the thrust from the connecting rods and it provides a rotary movement from the reciprocating rectilinear movements of the pistons.

Conventionally, the crankshaft of an internal combustion engine has shaft seats, or journals, placed in line along the axis of rotation of the crankshaft and which are intended to come to rotate in associated complementary bearings of the engine.

The crank pins constituting the axes of the connecting rod heads are secured to pins by pairs of arms extending substantially perpendicular to the longitudinal axis of the crankshaft.

In addition, the crankshaft is provided with counterweights, also called unbalances used for the static and dynamic balancing of the moving parts constituted by the different crankpin-rod-piston assemblies.

Each counterweight is carried by at least one of the arms supporting the crankpin opposite the latter relative to the journal.

The problem of balancing crankshafts is particularly important. Indeed, from the point of view of mechanical forces, the crankshaft is the most stressed part of the engine. It supports in particular the forces due to positive or negative accelerations of the connecting rods and pistons, to the inertias of the eccentric masses and to the driving and resistant torques.

As a result, the crankshaft is subjected to significant torsional and bending forces which are transmitted to the engine block via the crankshaft bearings. Poor balancing can in particular lead to the production of significant vibrations, in particular at the level of the central bearing which is the most stressed due to the longitudinal deflection of the crankshaft along its axis of rotation, such vibrations being liable to cause the mechanical parts to rupture by fatigue. .

The balancing of the crankshaft is first obtained thanks to a particularly careful design of the part, notably using finite element calculations.

However, current techniques for manufacturing crankshafts (which are cast in GS cast iron or forged in steel, with recovery by machining the bearing surfaces) do not allow direct perfectly balanced parts to be obtained.

Examples of crankshaft designs are illustrated in documents FR-A1-2.720.809 and FR-A1-2.970.662.

Furthermore, current manufacturing processes result in globally massive parts for which it appears desirable to reduce their mass - and in particular the rotating mass - while retaining each crankshaft its balancing qualities ensured in particular by counterweights or unbalances .

Such a reduction in the weight or mass of the crankshaft makes it possible in particular to reduce the energy consumption of the vehicle.

The design of the counterweights must meet different requirements. They must first of all be correctly positioned in relation to the connecting rods, to best compensate for the inertial forces. They must be compact, so as to optimize the compactness of the engine. They must also allow the oil films, present at the connections between the crankshaft and the engine crankcase / cylinder block, to have a sufficient thickness at all points to lubricate these connections correctly. Finally, they must make it possible to reduce the noise generated by the engine.

The compromise generally used consists in making the crankshaft in a single piece from a single material, for example by casting in cast iron. This solution, chosen for the reduced cost of melting, does not however allow optimal results in terms of size.

For example, for competition engines, it has been proposed to make crankshafts of reduced dimensions, by gluing or screwing high density flyweights on its counterweights, at a distance from the axis of rotation of the crankshaft.

The use of such added weights has proven to be particularly effective. The manufacture of such crankshafts, on the other hand, is expensive and difficult to implement for mass production.

In the context of crankshaft production by molding, the publication US 2005/0266260 discloses a crankshaft molding process with the incorporation of components of different densities at different stages of molding. The molding comprises at least two molding phases to incorporate components of different densities.

The presence of balancing counterweights is also implemented by means of balancing shafts which include balancing blocks playing the same role as the counterweights of a crankshaft. An example of the design of such a balancing shaft is for example illustrated in the document FR-A1-2.823.279.

The mass production of such balancing shafts must also make it possible to reliably and precisely control the balancing problems.

Thus, the invention aims to propose a new design of a rotary shaft, and in particular of a crankshaft or a motor vehicle balancing shaft, of the type comprising:

- a main body which comprises at least two axially spaced sections for guiding the shaft in rotation;

- And at least one block for balancing the masses of the rotary shaft relative to its axis of rotation, in which the balancing block comprises:

- a central part for connection to at least one guide section;

- and a main part forming a counterweight which is connected to the central connection part and which is radially eccentric with respect to the axis of rotation of the rotary shaft, which overcomes the problems mentioned above.

BRIEF SUMMARY OF THE INVENTION

The invention provides a rotary shaft of the type mentioned above, characterized in that at least a portion of at least part of the balancing block is produced by an additive manufacturing technique.

According to other characteristics of the rotary shaft:

- At least a portion of at least part of the balancing block produced by an additive manufacturing technique is a portion comprising empty zones;

- the portion comprising empty zones is a portion of the central connection part of the balancing block;

- at least a part of the outer envelope surface of the portion comprising empty zones is a part of full surface;

- at least a part of the outer envelope surface of a portion of the balancing block produced by an additive manufacturing technique is a part of a non-smooth surface;

- On the one hand the main body and, on the other hand, said at least a portion of the balancing block produced by an additive manufacturing technique, are made of different materials;

- the entire main part forming a counterweight to the balancing block is produced by said additive manufacturing technique;

- a component, belonging to a detection and / or measurement system of at least one rotation parameter of the rotary shaft, is embedded in a portion produced by said additive manufacturing technique;

- the additive manufacturing technique is for example a laser deposition technique;

- The additive manufacturing technique is for example a powder bed melting technique; the shaft, for example the crankshaft can be produced entirely by fusion on a powder bed; in this case, the manufacturing is carried out entirely from powder, without connection or connection with another part produced according to another manufacturing technique, production such as for example the foundry or the forge;

- The shaft is a balancing shaft of a combustion engine capable of being rotatably mounted in a casing and / or a block and which is linked in rotation to a crankshaft of the combustion engine.

- The shaft is a crankshaft of a combustion engine capable of being rotatably mounted in a casing and / or a block of the combustion engine.

The invention also provides a method of manufacturing a rotary shaft according to the invention, characterized in that it consists in producing the main body, by forging or by molding, then in producing at least a portion of at least one part of the balancing block by an additive manufacturing technique.

The invention also provides a combustion engine, in particular for a motor vehicle, characterized in that it comprises at least one rotary shaft according to the invention, and in particular a crankshaft and / or a balancing shaft.

BRIEF DESCRIPTION OF THE FIGURES

Other characteristics and advantages of the invention will appear during the reading of the detailed description which will follow for the understanding of which reference will be made to the appended drawings in which:

- Figure 1 is a schematic perspective view of an exemplary design of a crankshaft according to the prior art;

- Figure 2 is a schematic sectional view along a median radial plane of the front axial end counterweight of the crankshaft of Figure 1;

- Figure 3 is a schematic side view of a section of the crankshaft of Figures 1 and 2;

- Figure 4 is a view similar to that of Figure 3 which illustrates the implementation of the teachings of the invention;

- Figure 5 is a schematic axial view at the end of the section illustrated in Figure 3;

- Figure 6 is a schematic axial view at the end of the section illustrated in Figure 4;

- Figure 7 is a view similar to that of Figure 4 illustrating a step of making a counterweight by additive manufacturing by laser deposition;

- Figure 8 is a view similar to that of Figure 4 illustrating an alternative embodiment;

- Figure 9 is a view similar to that of Figure 4 illustrating another alternative embodiment comprising a component, belonging to a detection and / or measurement system of at least one parameter of rotation of the crankshaft;

- Figures 10A to 10C schematically illustrate the stages of progressive manufacturing by implementing the technique known as melting on a powder bed.

DETAILED DESCRIPTION OF THE FIGURES

In the following description, elements having an identical structure or analogous functions will be designated by the same references.

In the following description, longitudinal, vertical and transverse orientations indicated by the trihedron L, V, T in the figures will be adopted without limitation.

The axis of rotation of the crankshaft is oriented parallel to the longitudinal direction, and from back to front.

In Figure 1, there is shown schematically a crankshaft 100 of an internal combustion engine.

This internal combustion engine, not shown in the figures, here comprises four cylinders which each house a piston which is adapted to slide along the internal wall of this cylinder according to a reciprocating rectilinear movement (or reciprocating movement) .

Each piston has for this purpose a peripheral skirt which slides in the cylinder. This skirt is pierced transversely with two openings for receiving an axis on which a high end called the foot of a connecting rod is mounted for rotation.

As shown in fig 1, the crankshaft 100 for its part comprises a main body in the form of a shaft 101 which defines four cranks 104 regularly spaced from one another, on which the lower ends of the connecting rods, called connecting rod heads, can be rotatably mounted.

Thus, the reciprocating rectilinear movement of the pistons makes it possible to drive the crankshaft 100 in rotation about the axis A of its shaft 101.

We then say of the crankshaft 100 that it comprises four crank pins 104 (the cranks) which are interposed between five pins 105. Each crank pin 104 is a cylindrical section.

The pins 105 are adapted to be engaged in complementary concave cylindrical openings provided in correspondence in the cylinder block of the engine, so as to form rotary connections for the crankshaft 100.

Each pin 105 is thus a section of the shaft 101 for guiding the latter in rotation.

While the pins 105 are aligned along the axis, A also called the motor axis, the crank pins 104 extend along axes parallel and distinct from the motor axis A (at a distance called the crank radius).

The crank pins 104 and the pins 105 are connected to each other by transverse flanges 103.

Opposite each crankpin 104, the shaft 101 of the crankshaft 100 further carries a balancing block called a counterweight 106 (also called an unbalance) making it possible to reduce the vibrations (in bending and / or in torsion) due to movements. of the movable coupling which includes the crankshaft, the connecting rods and the pistons.

The crankshaft 100 thus comprises two counterweights arranged at the front and rear axial ends, and two “central” counterweights arranged substantially at mid-length of the crankshaft 100, between two pairs of pistons.

Each of these four counterweights 106 has the general shape of a thick disc arc which extends over a determined angular sector.

For each counterweight 106, it is then possible to define an external surface of the counterweight which comprises the two substantially planar faces of radial orientation and axially opposite 107, and the edge 108 in an arc of a circle of the thick disc arc.

In the design example illustrated in FIGS. 1 and 2, the crankshaft is produced homogeneously from a single metallic material, for example by molding and / or forging and by complementary machining.

As can be seen in particular in Figure 2, each counterweight is thus in one piece "homogeneous" with a continuity of material.

It can also be seen that the counterweight comprises a main part PPC forming a counterweight which is the most radially eccentric portion, and a central part PCR for connecting the main part PPC to at least one adjacent guide pin 105.

According to the invention, as illustrated in FIG. 4, and by comparison with FIG. 3, the counterweights 106 are no longer produced "in one piece" with the main body comprising in particular the pins 105, that is to say that - for all or part - each counterweight 106 is no longer produced at the same time and according to the same production technique such as for example molding and / or forging.

At least a portion 200 of the counterweight 106 is produced independently of the main body using a technique called additive manufacturing also called "additive manufacturing".

In the examples illustrated diagrammatically in FIGS. 4 and 6 to 9, the portion 200 corresponds substantially to the central PCR part for connecting each counterweight.

As can be seen in Figure 7, the main body is for example made by forging, then begins the step of making each counterweight 106 by progressive addition of material, here according to the laser deposition technique, also called "laser cladding "

For example, the deposition uses a laser beam which is defocused on the part with a determined spot size. The deposition material, for example in powder form, is transported by an inert gas through a powder nozzle in the molten bath.

The laser optics and the nozzle are moved according to programmed movements so as to gradually deposit superimposed layers of greater or lesser volume.

The material supplied can also be used as a filler instead of the powder.

The manufacturing technique or techniques used in the context of the invention directly provide the connection between a part initially produced by molding, forging and / or machining, and the portion 200.

In the example illustrated in FIGS. 4 and 6 to 9, the portion 200 connects the main body with in particular the pins 105, to the main PPC part which is here produced by implementing a conventional manufacturing technique of molding, forging. and / or machining.

As shown diagrammatically in FIGS. 4 and 6 to 9, developments in additive manufacturing techniques, and in particular in laser deposition, make it possible to produce parts or portions or parts in a material comprising voids.

This is particularly the case when the portion 200 is produced in the form of an architectural structure composed of a material and of empty areas, for example in the form of a lattice - or "lattice" in three dimensions.

In this case, the density or density of the portion produced by additive manufacturing is less than the mass of the corresponding portion which would be produced "full".

In the context of producing a counterweight 106, it is thus possible to obtain a reduction in the total mass of each counterweight, and therefore of the crankshaft.

As part of the complete production of a crankshaft 100 by a powder bed fusion technique, as illustrated in FIGS. 10A to 10C, the lightening is carried out by creating voids during construction. The powder fused by the laser beam in the lightened area can have a three-dimensional lattice or "lattice" structure.

As shown diagrammatically in FIGS. 5 and 6, the invention makes it possible to “adjust” with precision the position of the center of gravity of the counterweight 106 whose function is the balancing of the masses in reciprocating motion of the piston-rod assembly.

The inertial force of the counterweight being proportional to the product of the mass of the counterweight by the distance AG of the axis of rotation A to the center of gravity G of the counterweight 106, the balancing is identical to that of the crankshaft with full counterweight when the mass x AG product is kept on the light version.

The reduction in mass is then offset by the increase in the distance AG.

When the main body without counterweight, that is to say before adding material by additive manufacturing, is carried out by forging, this production step requires less shaping effort because its geometry is simpler. There is also less material engagement.

When the portion 200 is not full, the portion can be "closed" to form a continuous external surface of the counterweight. This is illustrated schematically in Figures 8 and 9 in which there is illustrated the addition of an outer layer 202 "full" or "closed".

The surface state of this closure layer 202 can be non-smooth and for example textured, for example, to improve the cooling of the lubricating oil by local stirring promoting heat exchange.

Such an achievement is easy by implementing additive manufacturing techniques.

As shown schematically in Figure 9, the implementation of an additive manufacturing technique easily allows the integration of a component 204 in a portion or area of a counterweight 106 produced by additive manufacturing.

Such a component 204 belongs for example to a system (not shown) for measuring parameters representative of the rotation of the crankshaft (speed, acceleration, etc.).

Examples of steps in a complete manufacture of a crankshaft 100 by the additive manufacturing technique known as powder bed fusion are illustrated diagrammatically in FIGS. 10A to 10C.

The views of the crankshaft 100 are "transparent" through the powder 302. The powder not fused by the laser beam 304 is removed after manufacture.

A layer of powder 302, of the order of a few tens of micrometers thick, is added to the previous layer, or to the plate 300 as regards the deposition of the first layer).

It is fused by the laser beam 304 according to the desired geometry of the final part.

The plate 302 is translated downwards before each addition / deposit of a new layer.

The use of additive manufacturing techniques also makes it possible to combine different materials in the production 5 of a counterweight 1 06.

Claims (13)

1. Rotary shaft (100) comprising: - A main body (101) which comprises at least two sections (105) spaced axially guiding in rotation of the shaft (1 00); - And at least one block (106) for balancing the masses of the rotary shaft (100) relative to its axis (A) of rotation, in which the balancing block (106) comprises: - a central part (PCR) for connection to at least one guide section (105); - And a main part (PPC) forming a counterweight which is connected to the central part (PCR) of connection and which is eccentric radially with respect to the axis (A) of rotation of the rotary shaft (1 00), characterized in that at least a portion (200) of at least a portion (PCR) of the balancing block (106) is produced by an additive manufacturing technique. 2. Rotary shaft (100) according to claim 1, characterized in that at least a portion (200) of at least part of the balancing block (106) produced by an additive manufacturing technique is a portion (200 ) with empty areas. 3. Rotary shaft (100) according to claim 2, characterized in that said portion (200) having empty areas is a portion of the central part (PCR) for connection of the balancing block (1 06). 4. Rotary shaft (100) according to one of claims 2 or 3, characterized in that at least a part of the outer casing surface (202) of said portion (200) having empty areas is a surface part full. 5. Rotary shaft (100) according to any one of the preceding claims, characterized in that at least part of the outer casing surface (202) of a portion (200) of the balancing block (106) produced by an additive manufacturing technique is a non-smooth surface part. 6. Rotary shaft (100) according to any one of the preceding claims, characterized in that the entire main part (PPC) forming a counterweight to the balancing block (106) is produced by said additive manufacturing technique. 7. rotary shaft (100) according to any one of the preceding claims, characterized in that a component (204), belonging to a detection and / or measurement system of at least one parameter of rotation of the shaft rotary (100), is embedded in a portion produced by an additive manufacturing technique. 8. Rotary shaft (100) according to any one of the preceding claims, characterized in that said additive manufacturing technique is a laser deposition technique. 9. rotary shaft (100) according to any one of the preceding claims, characterized in that on the one hand the main body (101) and, on the other hand, said at least one portion (200) of the balancing block (106) made by an additive manufacturing technique, are made of different materials. 10. Shaft according to any one of the preceding claims, characterized in that it is a balancing shaft of a combustion engine capable of being rotatably mounted in a casing and / or a block and which is linked in rotation to a crankshaft of the combustion engine. 11. Rotary shaft (100) according to any one of the preceding claims, characterized in that it is a crankshaft (100) of a combustion engine capable of being rotatably mounted in a casing and / or a block of the engine. combustion. 12. A method of manufacturing a rotary shaft according to any one of the preceding claims, characterized in that it consists in producing the main body (101), by forging or by molding, then in producing at least a portion (200 ) at least part of at least one balancing block (106) by said additive manufacturing technique. 13. Combustion engine, especially of a vehicle 5 automobile, characterized in that it comprises at least one rotary shaft (100) according to any one of claims 1 to 12.