WO2011045504A1

WO2011045504A1 - Crankshaft for an internal combustion engine

Info

Publication number: WO2011045504A1
Application number: PCT/FR2010/052109
Authority: WO
Inventors: Laurent Bechu; Jean-Yves Morin; Martine Monin
Original assignee: Peugeot Citroën Automobiles SA
Priority date: 2009-10-14
Filing date: 2010-10-07
Publication date: 2011-04-21
Also published as: FR2951236B1; FR2951236A1

Abstract

The invention relates to a crankshaft (1) for an internal combustion engine and involves said crankshaft (1) having an outer metal casing (2) surrounding a plastic core (4). The invention is of use for engine crankshafts.

Description

Crankshaft for internal combustion engine

The present invention claims the priority of the French application 0957181 filed October 14, 2009 whose content (text, drawings and claims) is here incorporated by reference.

[Ooo2] The invention relates to a lightened crankshaft for an internal combustion engine, an engine and a vehicle equipped with this crankshaft and the method of manufacturing such a crankshaft.

[ooo3] The crankshafts that equip the engines of today's vehicles are generally manufactured in one piece, for example press-forged or cast. The material used, such as cast iron and steel, is therefore present in all the sections of the part, which necessitates carrying out, during the machining operations, passage orifices for the oil which makes it possible to lubricate the bearings and the crank pins present on the crankshaft. Depending on the motorization more or less solicited, the criteria of resistance make crankshafts choose either cast iron or forged steel.

[ooo4] Crankshafts are parts subjected to bending stresses which are concentrated in the connection grooves (rod forces), torsional stresses which mainly stress the center of the trunnions and the grease orifices, to stresses of stress. torsional and bending vibrations as well as wear of bearings and crank pins or antagonistic materials in relation to lubrication.

[Ooo5] Due to the solid shapes of such a crankshaft, it usually has a significant weight that it is not possible to reduce without affecting the geometry and dimensions of the outer forms of the crankshaft.

[ooo6] In order to reduce the mass of a crankshaft, it has been proposed to remove material in the center of the crank pins and trunnions, the material in these areas being uneconomical in terms of rigidity and strength of the piece.

[0007] In EP 1 767 288 has thus been proposed a hollow crankshaft obtained by molding. In order to reduce the weight of such a part, it has been proposed in FR 2 802 591 to produce a mechanically welded crankshaft consisting of a number of individual elements provided with cavities in their interior and assembled to each other. to form the crankshaft. The individual elements are thus assembled by welds extending transversely to the axis of the crankshaft.

[0009] A relatively similar manufacturing process has been proposed in DE 1 95 36 349, the individual cavity-provided elements being assembled by friction welding.

[ooi o] However, despite certain advantages in terms of weight gain due to the hollow nature of crankshafts thus produced, then poses a problem related to the lubrication circuit as with most of the proposed hollow crankshafts. Thus, the volume inside such a hollow crankshaft defines a volume for the much larger lubrication circuit, making it necessary to use a new oil pump to overcome the increase in oil volume. Moreover, it is necessary to ensure a good filling of the hollow zones by the oil in order to properly lubricate the bearings and crank pins. In addition, one can also have a cleanliness problem and a risk of retardation of rise in pressure of the oil at the start of the engine.

[ooi i] In addition, for crankshafts consisting of individual welded elements, there is a risk in terms of welding performance and quality.

It was then proposed to make a hollow crankshaft obtained by casting, a metal tube being inserted into the mold to form a main channel extending axially while tubes connect this channel outside the crankshaft. Therefore, after casting, the crankshaft thus formed has a main channel of lubrication to the bearings and cranks through the tubes. However, such a manufacturing method only allows crankshafts overlap and in addition, during casting, it can occur deformations of the tube generating circulation difficulties in the lubrication circuit can then lead to poor performance of the crankshaft related to lower quality lubrication. Also, the present invention aims to propose a crankshaft "lightened" so to have a gain in mass while preserving within this lightweight crankshaft, a lubrication system that efficiently and optimally lubricates the bearings and crank pins.

For this purpose, the present invention relates to a so-called lightweight crankshaft, characterized in that it has a metal outer envelope surrounding a core made of a plastic material.

Thus advantageously, there is provided a lightened crankshaft since only the outer casing is metal while the inner portion of said crankshaft is made of a chosen plastic material lighter than metal, which allows a gain in mass while by offering the possibility of creating within said plastic material present in all sections of the part, a lubrication circuit thus making it possible to overcome the disadvantages of hollow crankshafts.

The outer casing made of a metal material may be forged steel, cast steel or cast iron.

The plastic material constituting the core is selected from plastics compatible in terms of thermal and chemical resistance with hot engine oil based: polyamide type (such as PA6, PA66, PA46, PA6-66 , ...), of polyphthalamide type (such as PA6T / 66, PA6T / 6I), of polybutylene terephthalate (PBT) type, copolyester or copolyether type.

Advantageously, the bi-material crankshaft thus produced may have a conventional internal lubrication circuit for lubricating the bearings and crank pins present on the crankshaft, a bore being formed to form a conduit between an adjacent bearing and an adjacent crankpin at the level of an arm connecting them, in a conventional way in itself. The circuit thus consists of ducts connecting a bearing and a crankpin which respectively have a bore to the outside.

The present invention also relates to a method of manufacturing a crankshaft according to the invention in which a hollow metal outer shell is formed, it is injected into the plastic material, said metal outer shell acting as mold cavity filling said material and maintaining the pressure until all cooling said plastic material.

The formation of the hollow metal outer casing can be carried out for example by welding two half-shells obtained by forging, for example by stamping. Any other method for producing such an outer envelope is also usable.

According to a first embodiment, once the outer casing has been completed, the cavity formed by said casing is completely filled by means of a conventional injection method, at the end of the filling and filling phases. maintaining pressure during cooling of the plastic material, machining operations are carried out to generate channels and passage holes for the oil, for example at an arm, a duct connecting a bearing and a crankpin which also has bores outward. The pressure maintaining phase makes it possible to limit the size of the porosities associated with the removal of the material in the cavity of the hollow crankshaft during cooling.

In the case where the crankshaft designed has a height of the overlap area too low to allow a good passage of the plastic material injected over the entire length of the crankshaft, it is then proposed to make a hole at each zone and to inject at the level of each zone the necessary quantity of plastic to fill the cavities. This case is specific to a steel crankshaft made by welding 2 forged half-shells.

According to a second embodiment, the cavity defined by the outer metal shell is filled using an injection process coupled to a foaming or expanding process of a plastic material. Advantageously, such a foaming or expansion process makes it possible to limit the amount of material constituting the heart of the crankshaft thus allowing additional bulk lightening, a limitation of the large porosities and a homogenization of the material health. Then, using machining operations, channels and passage holes for the oil are generated as already mentioned.

According to a third embodiment, the cavity formed by the outer metal casing is filled using a gas-assisted and / or water-assisted plastic injection molding process. Such a method makes it possible to produce a hollow internal plastic body thus limiting the filling material, hence a gain in mass, but also making it possible to create a lubrication channel within the crankshaft thus produced. Then holes are drilled at the level of the bearings and cranks to come into communication with said channel and thus allow supplying said bearings and cranks with oil from the main channel passing through the crankshaft core.

The invention also relates to an engine equipped with such a crankshaft and a vehicle equipped with this engine.

We will now describe the invention in more detail with reference to the drawing in which:

[0027] Figure 1 shows a longitudinal sectional view of an outer crankshaft casing according to the invention;

[0028] Figure 2 shows a longitudinal sectional view of a crankshaft according to a first embodiment;

Figure 2a shows a partial longitudinal sectional view of a crankshaft having a low overlap area;

Figures 3 and 4 respectively show a longitudinal sectional view of a crankshaft obtained after filling of the plastic material according to the third embodiment.

As can be seen in Figure 1, a crankshaft 1 according to the invention comprises a hollow metal outer shell 2 made for example by the assembly of two half-shells stamped and welded. These two half-shells can be made of steel "cast or forged" or cast iron. Then the metal hollow body 2 is optionally preheated and the cavity 3 thus defined is filled with plastic. Compared with the injection of a completely plastic part, the hollow metal crankshaft 2 here fulfills the role of impression of the filling mold, in this case that in this case the plastic part is not demolded.

Then use a standard plastic injection process. Thus, the cavity 3 defined by the casing 2 is completely filled with plastic material from one end of the casing 2, the other being closed, and then the pressure is maintained until the plastic material cools. This maintenance in pressure makes it possible to minimize the risks of porosities related to the withdrawal of the material. This forms the core 4 of the crankshaft 1. Depending on the thickness of the cavity that is to say the envelope 2, which may vary depending on the crankshaft 1 envisaged, there may be a risk of creating core porosities ( as can be seen on some plastic parts used in cars and with massive areas). However, this should not pose any functional problems.

The difference in expansion between the two materials (metal and plastic) is not a problem, the only consequence being the risk of infiltration of oil between the two materials but without affecting the operation of the piece 1 thus produced.

The crankshaft 1 bi-material "non-hollow" but lightened can then be drilled, so as to obtain a traditional lubrication circuit of the bearings and crank pins similar to a lubrication circuit of a conventional crankshaft (not shown in FIG. 2). The plastic does not pose any particular difficulty at the time of machining because such a material is not hard.

In the case where the crankshaft 1 designed has a height of the overlap zone R too low to allow a good passage of the plastic material injected over the entire length of the crankshaft 1 a (as in the previous example), the two half-shells 2 being in contact in this zone R, it is then proposed to make a hole 6 at each zone 7 to be filled with plastic material 4 and to inject at each of these zones 7 the necessary quantity of plastic material 4 to fill the cavities as can be seen in Figure 2a. This case is specific to a steel crankshaft made by welding two forged half-shells. As a result, the end portion of the shell 8 remains hollow without plastics inside. The lubrication holes are then drilled as in the case of making a full crankshaft. Areas remaining hollow may exist, and will not be filled with plastic, because these areas are not crossed by any lubrication channel

The casing 2 'of the crankshaft 1' of Figure 4 is also a hollow metal shell, either forged steel, or cast steel, or cast iron. The core 4 'of the crankshaft is filled with a plastic material compatible in terms of thermal and chemical resistance with hot engine oil, for example of the polyamide type (PA6, PA66, PA46, PA6-66, etc.), of the PPA polyphthalamide type. (PA6T / 66, PA6T / 6I, ...) or PBT type. In addition, as can be seen in Figures 4 and 5, the heart of the core 4 'of plastic is hollow. Indeed, after completion of the casing 2 'of the crankshaft 1', the metal hollow body 2 'is optionally preheated and the cavity 3' thus defined is filled using a gas assisted assisted injection process water. Thus, the plastic is injected into the mold formed of the outer shell 2 ', then gas is injected in the center of one of the ends of the piece, and the injected gas creates a central duct 5' free of plastic, thus creating a channel 5 'of lubrication inside the crankshaft 1'.

Such a manufacturing method is applicable to crankshafts having a lap area between the crank pins and bearings, large enough to allow continuous filling with a hollow zone all along the piece.

Such a crankshaft 1 'can then be drilled (see Figure 4), so as to supply oil bearings and crankpins from the main channel 5' through the heart of the crankshaft '. The plastic does not pose any particular difficulty when machining these small holes 6 '.

The invention thus allows to obtain lightened crankshafts with weight gains varying according to the plastic filling material used. Thus, the density of the PA6 is, according to the grades, between 1040 and 1150 kg / m3 and the density of the PA66 is, according to the grades, between 1140 and 1150 kg / m3 whereas for comparison the density of the PA6 is a GS cast iron used on crankshafts is equal to 7200 kg / m3 and the density of the steel is 7850 kg / m3. The density ratio between the melt and PA6 is equal to 7200/1 100 or 6.5 and that between steel and PA6 is equal to 7850/1 100 or 7.1. So we have a gain in mass of the crankshaft of about 10%.

In addition, the hollow areas of the crankshaft 1 being filled with plastic, they can not be filled by the lubricating oil and there is no new oil pump to provide.

In addition, it eliminates the impact of the evolution of the hollow areas according to the wear of stamping tools. Furthermore, there is no incidence of balancing of the crankshaft engine operation because of the absence of oil in the hollow areas or even risk of calamine resulting from welding in the oil circuit. This eliminates the risk of delay of the rise in oil pressure during engine start.

Claims

claims

1. Crankshaft (1, 1 ') for an internal combustion engine, characterized in that it has a metal outer shell (2, 2') surrounding a core (4, 4 ') made of a plastic material.

2. Crankshaft (1, 1 ') according to claim 1, characterized in that the outer casing (2, 2') is made of a metallic material such as forged steel, cast steel, cast iron.

3. crankshaft (1, 1 ') according to one of claims 1 and 2, characterized in that the plastic material constituting the core (4, 4') is selected from plastics compatible in terms of thermal and chemical resistance with hot engine oil on base: of polyamide type such as PA6, PA66, PA46, PA6-6, of polyphthalamide type such as PA6T / 66, PA6T / 6I, of polybutylene terephthalate (PBT) type, copolyester type or copolyether.

4. Crankshaft (1) according to one of claims 1 to 3, characterized in that it comprises a lubrication circuit consisting of ducts connecting a bearing and a crankpin which respectively have a bore to the outside.

5. crankshaft (1 ') according to one of claims 1 to 3, characterized in that it comprises a lubrication circuit comprising a main channel (5') extending through the core (4 ') in plastic material of the crankshaft (1 '), bores (6') connecting the main channel (5 ') to the outside at the bearings and crankpins.

6. A method of manufacturing a crankshaft (1, 1 '), characterized in that a hollow metal outer shell (2, 2') is formed, said plastics material is injected into said outer metal shell (2, 2 ') acting as a filling mold cavity for said material and the whole is kept under pressure until the cooling of said plastic material.

7. Method according to claim 6, characterized in that the hollow metal outer casing (2, 2 ') is made by welding two half-shells obtained by forging.

8. Method according to one of claims 6 and 7, characterized in that once the outer casing carried out, completely filling the cavity formed by said casing using a conventional injection method, the the result of the filling and pressurization phases during the cooling of the plastics material, it is possible, by means of machining operations, to make passage openings for the oil, such as at the level of an arm, a conduit connecting a bearing and a crankpin which respectively have a bore to the outside.

9. A method according to claim 8, characterized in that a bore (6) is made at each zone (7) to be filled with plastic material and injected at each of these zones (7) the necessary quantity. of plastic material (4) for filling the cavities, at the end of the filling and pressurizing phases during the cooling of the plastic material, it is possible to carry out, through machining operations, passage orifices for oil, such as at an arm, a duct connecting a bearing and a crankpin which respectively have a bore to the outside.

10. Method according to one of claims 6 and 7, characterized in that the injection process is coupled to a foaming process or expansion of a plastic material.

1 1. Process according to one of Claims 6 and 7, characterized in that the cavity formed by the outer metal shell (2 ') is filled by means of a gas assisted injection process and / or assisted by water, making it possible to produce a core (4 ') of hollow internal plastic material forming a lubrication channel (5') inside the crankshaft (1 ') thus produced, then holes (6') are drilled at the level of the bearings and crank pins for communicating with said channel (5 ').

12. Engine equipped with a crankshaft according to one of claims 1 to 5.