FORM 2
THE PATENTS ACT 1970
(39 of 1970)
&
The Patent Rules, 2003
Complete Specification
(See section 10 and rule 13)
A Hollow Crankshaft and Method of Manufacturing It
Bharat Forge Limited
An Indian company registered under the Indian Companies Act, 1956. Mundhwa, Pune - 411036, Maharashtra, India
CSIR- Central Mechanical Engineering Research Institute
Mahatma Gandhi Avenue, Durgapur 713209, West Bengal, India
Fraunhofer Gesellschaft
Reichenhainer Straße 88, 09126 Chemnitz, Germany
The following specification particularly describes the invention and the manner in which it is to be performed

Field of invention:
The present invention relates to crankshaft for use in automobile industry or in power generators, or in any other industry where a crankshaft is required. More particularly, the present invention relates to providing a hollow and lightweight crankshaft without affecting its performance characteristics. The present invention also relates to a process of manufacturing hollow crankshafts.
Background of invention:
A crankshaft is the vital part of an engine. It converts reciprocating motion of a
piston into rotational motion. It rests on main bearings provided inside a
crankcase. A crankshaft – the main parts of which are crank pins, crank journals,
crank webs, counterweights, a tail end and a flange end – is a part with complex
geometry.
Figure 1 shows a typical conventional 4-cylinder crankshaft (1). Figures 2 and 3 show respectively a single throw and single half throw of conventional crankshaft. In case of conventional crankshafts, the tail end or gear end is connected to a gear box while the flange end is connected to the flywheel. One end of the typical crank pin (pin) is connected to one end of a crank web (web) which may be provided with or without a counterweight (CW), while the other end of web is connected to one end of a crank journal (journal). The other end of the journal is connected to another web’s one end, and the other end of this web is connected to another crank pin. In case of V-Engine, the one end of first crank pin is connected

to one end of second crank pin, while the other ends of first and second crank pins are connected to two ends of different webs. A piston is connected to each of the respective crank pins. The journals rest on main bearings. There are also the oil holes that are provided in pins and journals for lubricating purpose. The number of pins of a crankshaft determines the number of cylinders of an engine – for example, a crankshaft having four pins is typically called a 4-cylinder crankshaft and used in a 4-cylinder engine. A single throw of a typical crankshaft consist of one pin, two journals, and two webs which comes with or without a counterweight. A single throw of a V-Engine crankshaft consist of two pins (adjacent to each other), two journals, and two webs which comes with or without a counterweight.
There are several methods available for producing a conventional crankshaft. The popular methods include forging (followed by machining), or casting (followed by machining), and billet machining or carving route. Forging is the preferred manufacturing method employed in automotive industry or any industry where crankshaft is required, as it results in reduced material waste and high fatigue strength. The crankshafts used in automotive industry or any industry where crankshaft is required are typically forged in one piece while the large crankshaft employed in other applications are typically manufactured (forged) piece-by-piece and then bolted or joined by a suitable joining process.

Environment protection agencies world over are pressing for a reduction in overall carbon footprint. They are enforcing strict norms on pollutant emission. This has greatly affected automotive and related industries whose products still, by-and-large, run on fossil fuels. Development of lightweight vehicles without compromising the performance remains an ongoing quest for the automotive industry. This demands downsizing of the engine, transmission and chassis components without compromising its strength. Engine development remains at the center of the efforts of vehicle light weighting.
In a typical automotive engine, which consists of components such as a crankshaft, a connecting rod, bearings, a camshaft, crankcase, and an engine block and so on, the crankshaft weighs around the 11% of total weight of the engine. Any downsizing of the crankshaft will results in increased fuel efficiency and reduced carbon foot print.
The crankshaft can be light weighted by reducing the material from the non-design areas like the web and the counterweight.
There are a number of patents (or patent applications) available which claim to provide ways of doing this. Some of these focus on light-weighting of one-piece crankshafts made by forging techniques, but these have limited scope. These methods advocate removal of material from the pin, journal, web or the counterweight by machining after the forging stage. However, this results in

substantial material wastage and least amount of light-weighting. These types of light-weighting methods are found to further reduce a crankshaft’s strength and stiffness. Another patent application discloses a casting and joining method. They claim to have achieved substantial material savings but the crankshaft made by casting and which uses welding as the joining method is known to show poor fatigue performance. As a crankshaft continuously works under cyclic load, fatigue performance is a crucial parameter for a crankshaft.
These and several other problems hamper the development of the light weight crankshafts. There is therefore a need to provide a crankshaft which is light weight and which does not compromise it strength at critical sections or vehicular performance.
Objects of invention:
One object of the invention is to provide a light weight crankshaft or hollow
crankshaft.
Another object of the invention is to provide method to manufacture the light weight crankshaft or hollow crankshaft.
Another object of the invention is to provide a light weight crankshaft that incorporates hollowed out areas at pins and journals.

A further object of the invention is to provide hollow crankshaft for use in automotive and other industries, which improves the material utilization, reduces carbon footprint and increases fuel economy.
Another object of the invention is to provide hollow crankshaft that meets the industry specifications related to bending and torsion rigidities, stresses, bending compensation etc.
Yet another object of invention is to provide manufacturing method for the Hollow Crankshaft, whose pin and journal are hollow.
Yet another object of the invention is to provide joining method for joining the hollow pin and journals of hollow crankshaft.
Still another object of the invention is to provide the hollow crankshaft for automobile with least number of counterweights.
Yet another object of the invention is to provide the hollow crankshaft with light-weighting features/ pockets in the counterweights.
Yet further object of the invention is to provide low stress joining location of pins and journals of the hollow crankshaft.

A still further object of the invention is to provide a forging method of making light weight crankshafts which does not adversely affect the crankshaft performance characteristics.
Brief description of figures:
Figure 1 shows a schematic of conventional 4-cylinder crankshaft
Figure 2 shows a schematic of single throw of a typical conventional crankshaft
Figure 3 shows a schematic of half single throw of a typical conventional
crankshaft
Figure 4 shows a schematic of 4-cylinder hollow crankshaft of the invention
Figure 5 shows a schematic sectioned view of 4-cylinder hollow crankshaft of the
invention
Figures 6a, 6b, 6c and 6d show schematic of solid variations of half single throws
of hollow crankshaft of the invention
Figures 7a, 7b, 7c, and 7d show schematic of hollow variations of hollow half
single throws of hollow crankshaft of the invention
Figure 8 shows schematic side views of solid variations of half single throws of
hollow crankshaft of the invention
Figure 9 shows schematic side views of hollow variations of hollow half single
throws of hollow crankshaft of the invention
Figure 10 shows schematic of hollow variation of hollow tail end of hollow
crankshaft of the invention
Figure 11 shows schematic of hollow variation of hollow flange end of hollow
crankshaft of the invention

Figure 12 shows schematic of solid variations of solid tail end of hollow crankshafts of the invention
Figure 13 shows schematic of solid variations of solid flange end of hollow crankshafts of the invention
List of parts:
1 – Crankshaft 5 – Counterweight (or CW)
1a – Hollow crankshaft 5a – recess or pocket or light
2 – Crank pin (or pin) weighting feature in the
2a – solid pin of partial length counterweight
2b – first wall thickness 25 6 – Oil hole (or oil passage)
2ah – Hollow pin of partial length 7 – Hollow tail end
2h – hollow pin 7a – Solid tail end
3 – Crank journal (or journal) 8 – Hollow flange end
3a – solid journal of partial length 8a – Solid flange end
3b – second wall thickness 30 9 – solid half single throw
3ah – Hollow journal of partial 9a – hollow half single throw
length 10 – Single throw
3h – hollow journal 11 – Electron beam welding location
4 – Crank web (or web)
Summary of invention:
The invention discloses a light weight crankshaft or hollow crankshaft (1a) as shown in Figure 4 in which the crankshaft is manufactured by joining together individual hollow half single throws (9a), hollow tail end (7) and hollow flange end (8) and as such is distinguished from the existing solid crankshafts (1) by the transverse joints at hollowed pins and journals.
Each individual solid half single throw (9) comprises a web with or without counterweight, a journal of partial length (3a) and a pin of partial length (2a),

which are later hollowed out to form a hollow half single throw (9a), such that after joining together of any two such hollow half single throws (9a), a hollow pin or a hollow journal (2h and 3h) of full length between any two webs with or without counter weight is obtained.
In an embodiment of the invention, number of parts of the crankshaft (1) are hollowed out (Figure 4), particularly at least one journal and/or at least one pin. The counter weights may also be provided with a recess or pocket or light weighting feature (5a). The invention also discloses a method of manufacturing such crankshafts. Hollow half single throws (9a) are manufactured by forging (Figures 7a, 7b, 7c, and 7d ) wherein specific parts are hollowed out in forging itself or manufactured by forging (Figure 6a, 6b, 6c and 6d) and then hollowed portions are made by machining. The method of manufacture comprises the step of joining together the hollowed out half single throws (9a) using a suitable joining method that does not compromise crankshaft strength at critical sections. Preferable joining method is electron beam welding (EBW).
Description of Invention
The present invention aims to overcome the aforementioned problems given in
background of invention.
For the purpose of this invention, unless specifically mentioned otherwise, all parts such as pins, webs, journals are taken to be solid. This is particularly so in

the context of the solid half single throw (9). For the purpose of the present invention, a half single throw is a single throw that contains only partial lengths of pins or journals. Also for the purpose of the present invention, a hollow half single throw (9a) is a half single throw in which at least one of the pins (2a) or the journals (3a) of the solid half single throw (9) is hollowed out.
As shown in Figure 4, a hollow crankshaft (1a) is light-weighted crankshaft made light in weight by making the pins (2), journals (3), tail end (7) and flange end (8) hollow, preferably their inner portions, and reducing the number of counter weights. Additionally, light-weighting features such as concave pockets or concave recesses (5a) (Figure 4 and 5) of any shape (circular, elliptical, rectangular, polygonal etc.) are incorporated in the conventional counterweights to further increase the light weighting percentage. The hollow crankshaft (1a) disclosed in the present invention is manufactured using forging, welding and machining operations.
As an example, consider (see Figure 4) a 4-cylinder hollow crankshaft (1a) which consists of hollow pins (2h) of first wall thickness (2b), hollow journals (3h) of a second wall thickness (3b), webs (4) that are optionally provided with counterweights (5 – optionally provided with recesses 5a), a hollow tail end (7), and a hollow flange end (8), and oil holes (6) as necessary. Alternatively only some of the pins/journals may be hollowed out.

In one aspect of the invention, as a part of the manufacturing process of the hollow crankshaft (1a) disclosed in the invention, first a hollow half single throw (9a) is produced by forging methods, and comprises:
1) a partial hollow pin (2ah) of first wall thickness (2b),
2) a partial hollow journal (3ah) of a second wall thickness (3b), and
3) a web (4) that is optionally provided with a counterweight (5) and recess (5a) or pocket or light weighting feature.
In another aspect of the invention, as a part of the manufacturing process of the hollow crankshaft (1a) disclosed in the invention, first a solid half single throw (9) is produced by forging methods. A solid half single throw (9) comprises:
1) a portion of one solid pin (2a),
2) a portion of one solid journal (3a), and
3) a web (4) that is optionally provided with a counterweight (5) and recess (5a) or pocket or light weighting feature.
A hollow half single throw (9a) is made from the aforementioned solid half single throws (9) by machining methods, and comprises:
1) a portion of one solid pin (2a) hollowed out into a partial hollow pin (2ah) of a first wall thickness (2b),
2) a portion of one solid journal (3a) hollowed out into a partial hollow journal (3ah) of a second wall thickness (3b), and

3) a web (4) that is optionally provided with a counterweight (5) and recess (5a) or pocket or light weighting feature.
As the hollow crankshaft (1a) is made by joining together a number of hollow half single throws (9a), it is inevitable that there will be joints where two hollow half single throws (9a) are joined – these are typically at partial hollow pins (2ah) and/or partial hollow journals (3ah). The length of a partial hollow pin and partial hollow journal (2ah and 3ah) provided on a hollow half single throw (9a) is determined by the desired location of the joint between any two hollow half single throws (9a), the desired location being determined by individual crankshaft’s technical design.
In one embodiment of the invention, the partial hollow pin (2ah) has a length less than the length of said hollow pin (2h), and the partial hollow journal (3ah) has a length less than the length of said hollow journal (3h).
As shown in Figures 6a, 6b, 6c, 6d, and Fig. 7a, 7b, 7c, 7d a number of variations are possible depending on the ultimate lengths of the partial hollow pins (2ah) and partial hollow journals (3ah) selected in a hollow half single throw (9a). Figures 6a, 6b, 6c, and 6d are showing schematic of variations of solid half single throw (9) which are manufactured by forging. These variants are further hollowed out to produce partial hollow pin (2ah) and partial hollow journal (3ah) by machining

operations to produce hollow half single throws (9a). Figure 8 shows the side views C and D of one of the variation of solid half single throws.
Fig. 7a, 7b, 7c and 7d show the variants of hollow half single throw (9a) having partial hollow pins (2ah) and partial hollow journals (3ah), which may be manufactured by forging or by machining of the solid partial length pins and journals (2a and 3a), or some of them may be manufactured by forging and others by machining. Figure 9 shows the side views C and D of one of the variation of hollow half single throws.
For a typical 4-cylinder hollow crankshaft (1a), eight such hollow half single throws (9a) are manufactured separately, either by using forging technique or a combination of forging and machining techniques. These hollow half single throws (9a) are then further joined by electron beam welding process or any suitable joining process at appropriate locations.
The joining of the individual hollow half single throws (9a) is carried out such that the finished hollow crankshaft (1a) has the required/same length of hollow pins (2h) and hollow journals (3h) between any two webs (4). The joining locations are the low stress zones which a hollow crankshaft (1a) may experience under the actual working conditions. These low stress zones are determined by virtual testing and validated by actual fatigue testing. The joining locations are positioned away from fillets of pins (2) or journals (3) and pin/journal oil holes

(6). The hollow tail end (7) part and hollow flange end (8) part are further manufactured either by forging technique or forging and machining techniques and joined by EBW or any suitable joining process at their respective journal ends of the hollow crankshaft (1a) of the invention. The hollow tail end (7) part and hollow flange end (8) part of the hollow crankshaft (1a) are different as compared to conventional crankshaft’s (1) tail end and flange end. The hollow tail end (7) part and hollow flange end (8) part of the hollow crankshaft (1a) consist of some portion of end journals (3) are manufactured by forging and are as shown in Figure 10 and 11.
In the preferred embodiment of the invention, the wall thicknesses (2b, 3b) of the hollow pins and journals (2ah, 3ah) in all individual hollow half single throws (9a) are same.
In one embodiment of the invention, the wall thickness (2b, 3b) of the hollow pins and journals (2ah, 3ah) in at least one individual hollow half single throws (9a) is different from at least one other individual hollow half single throws (9a).
The solid tail end (7a) part and solid flange end (8a) part consist of some portion of end journals (3) of hollow crankshaft (1a) are manufactured by forging and are as shown in Figure 12 and 13. The hollowed out portions are further made by machining operations to form hollow tail end (7) part and hollow flange end (8) part.

These end journal portions of hollow tail end (7) part and hollow flange end (8) part of the hollow crankshaft (1a) is connected to subsequent journal portion of a hollow half single throw (9a).
Figure 5 shows the section view AA of hollow crankshaft (1a). The different hatching pattern in section view AA of Figure 5 shows how the 8 half single throws (9a), hollow tail end (7) and hollow flange end (8) are joined together at transverse joints by Electron Beam Welding or any suitable joining process.
In an embodiment of the invention, only some of the pins or journals of a hollow crankshaft may be hollowed out.
In another embodiment, in the hollow crankshaft (1a), the partial hollow journal (3ah) and the partial hollow pin (2ah) of at least one hollow half single throw (9a) is connected by a continuous oil hole (6) such that the ends of said oil hole (6) open into the hollowed part of said partial hollow journal (3ah) and said partial hollow pin (2ah).
The invention also discloses a method of making a hollow crankshaft (1a) which includes the steps of:
- making hollow half single throws (9a) in required number, said hollow half single throws (9a) comprises a web (4) with or without a

counterweight (5), and a partial hollow pin (2ah) and a partial hollow journal (3ah)
- making hollow tail end (7), and hollow flange end (8) by forging and machining techniques
- joining together said hollow half single throws (9a) such a partial hollow journal (3ah) of one hollow half single throw (9a) is joined with the partial hollow journal (3ah) of another hollow half single throw (9a) such that the joined up journals (3ah) form a hollow journal (3h) of full length, and that hollow partial pin (2ah) of one hollow half single throw (9a) is joined the hollow partial pin (2ah) of another hollow half single throw (9a) such that the joined up pins (2ah) form a hollow pin (2h) of full length;
- joining hollow tail end (7), and hollow flange end (8) to the respective end partial hollow journal (3ah)
- final machining of said joined hollow half single throws (9a) to form said hollow crankshaft (1a).
As discussed previously, the joining of hollow partial pins (2ah) and hollow partial journals (3ah) is performed using an electron beam welding technique. It is also important to note that the step of forming hollow partial pins (2ah) and hollow partial journals (3ah) may be carried out prior to the step of joining together said hollow half single throws (9a). Finally, the method of making the hollow crankshaft also comprises the step of providing oil holes (6) connecting

said hollow journal (3h) and said hollow pin (2h) such that the ends of said oil hole (6) open into the hollowed parts of said hollow journal (3h) and said hollow pin (2h).
The hollow crankshaft (1a) produced by the method disclosed in the invention has been tested in various real life situations representing various technical specifications. Results of these testing suggest that the hollow crankshaft (1a) of the invention meets the required specification related to bending rigidity, torsional rigidity, bending stresses, torsional stresses, bending deflection, bearing reaction, etc.
The 4 cylinder hollow crankshaft (1a) of the invention is designed with help of 3D CAD modeling tool, finite element analysis and actual prototyping. Around 70 to 80 conceptual designs were generated using 3D CAD. These all designs were evaluated against the said specification. The wall thickness (2b, 3b) respectively of hollow pin (2ah) and hollow journal (3ah) are one of the main parameter in design of hollow crankshaft (1a). The optimum wall thickness is to be designed in such a way that it gives required percentage of light weighting and also the crankshaft of this wall thickness meets performance characteristics. The wall thickness of hollow pin and journal were tried from 4mm to 20 mm for this particular 4 cylinder crankshaft. The wall thickness in the range of 10 to 15 mm are found better in achieving real life situations representing various technical

specification for this particular 4 cylinder crankshaft. The wall thicknesses are selected or being determined based on individual crankshaft’s technical design.
The weight reduction of around 25 to 30 % is achieved by this hollow crankshaft design as compared to conventional crankshaft.
The electron beam welding process have various advantages over other conventional welding process like Laser beam welding, TIG, MIG, ARC welding etc.
. High depth to width ratio: In case of high depth application, conventional welding process requires many passes and high preheating temperature, whereas EBW permits deep penetration in a single pass. Electron beam welding is a fusion welding process for joining metals. It uses as the heat source a highly focused beam of electrons traveling at high velocity and having a high power density, which causes almost instantaneous local melting and vaporization of work-piece material. This produces a narrow and parallel area of fusion welding affected very little by heat (i.e. a very low heat affected zone - HAZ). This allows butt welding in single pass for material thickness ranging from less than 0.1 mm to greater than 200 mm. . Low distortion: EBW results in low distortion because of low heat input compared to conventional welding processes (except laser beam welding).

. HAZ As compared to laser beam welding, the thickness of HAZ is less
in case of EBW. . No contamination during the EBW . Very high electrical efficiency (99%) compared to laser beam welding (<
15%). . Electron beam weld structure had fine crystalline structure which
improves joint strength by 15-25%.
Technical Advancement and Economic Significance
. The present invention reduces the weight of the crankshaft by 25 to 30%
keeping its strength intact as compared to conventional crankshaft. . The present invention reduces the carbon footprint. . The present invention improves the fuel economy of a vehicle.
While the above description contains much specificity, these should not be construed as limitation in the scope of the invention, but rather as an exemplification of the preferred embodiments thereof. It must be realized that modifications and variations are possible based on the disclosure given above without departing from the spirit and scope of the invention. Accordingly, the scope of the invention should be determined not by the embodiments illustrated, but by the appended claims and their legal equivalents.

We claim:
1. A hollow crankshaft (1a), characterized in that said crankshaft comprises at least one web (4), at least one counterweight (5), at least one hollow pin (2h) having a first wall thickness (2b), at least one hollow journal (3h) of a second wall thickness (3b), hollow tail end (7), and hollow flange end (8), said crankshaft (1a) is made by joining together individually made hollow half single throws (9a), hollow tail end (7), and hollow flange end (8).
2. The hollow crankshaft (1a) as claimed in claim 1, characterized in that said hollow half single throw (9a) comprises a web (4), a counterweight (5), a partial hollow pin (2ah) and a partial hollow journal (3ah).
3. The hollow crankshaft (1a) as claimed in claim 2, characterized in said partial hollow pin (2ah) has a length less than the length of said hollow pin (2h).
4. The hollow crankshaft (1a) as claimed in any of claims 2 and 3, characterized in that said partial hollow journal (3ah) has a length less than the length of said hollow journal (3h).
5. The hollow crankshaft (1a) as claimed in any of claims 1 to 4, characterized in that said hollow half single throw (9a) being made using forging technique.
6. The hollow crankshaft (1a) as claimed in any of claims 1 to 4, characterized in that said hollow half single throw (9a) is made from a solid half single throw (9) comprising a solid pin of partial length (2a) and a solid journal of a partial length (3a), said solid half single throw (9) being made by forging.

7. The hollow crankshaft (1a) as claimed in any of claims 2 to 6, characterized in that at least one of said solid pin of partial length (2a) or said solid journal of partial length (3a) is hollowed out using machining technique.
8. The hollow crankshaft (1a) as claimed in any of claims 1 to 7, characterized in that at least one of said counterweights (5) is provided with a recess (5a).
9. The hollow crankshaft (1a) as claimed in claims 1 to 8, characterized in that said hollowing out of at least one pin and/or at least one journal is performed using a forging technique.
10. The hollow crankshaft (1a) as claimed in claims 1 to 8, characterized in that said hollowing out is performed using machining technique.
11. The hollow crankshaft (1a) as claimed in any of claims 7-10, characterized in that said recess (5a) is provided using a forging technique.
12. The hollow crankshaft (1a) as claimed in any of claims 7-10, characterized in that said recess (5a) is provided using a machining technique.
13. The hollow crankshaft (1a) as claimed in any of claims 1 to 12, characterized in that said joining of said hollow half single throws (9a) is performed using electron beam welding technique.
14. The hollow crankshaft (1a) as claimed in any of claims 2 to 13, characterized in that said partial hollow journal (3ah) and said partial hollow pin (2ah) of at least one hollow half single throw (9) is connected by a continuous oil hole (6) such that the ends of said oil hole (6) open into the hollowed part of said partial hollow journal (3ah) and said partial hollow pin (2ah).

15. The hollow crankshaft (1a) as claimed in any of claims 1-14, characterized in that said wall thickness (2b, 3b) of the hollow pins and journals (2ah, 3ah) in at least one individual hollow half single throws (9a) is different from corresponding components in at least one other individual hollow half single throws (9a).
16. A hollow crankshaft (1a) as claimed in any of claims 1-15, characterized in that the shape of recess (5a) in at least one counterweight (5) is different from the shape of the recess (5a) in another counterweight (5).
17. A method of making a hollow crankshaft (1a), characterized in that said method comprises the step of:

- making hollow half single throws (9a) in required number, said hollow half single throws (9a) comprises a web (4) with or without a counterweight (5), and a partial hollow pin (2ah) and a partial hollow journal (3ah);
- making hollow tail end (7), and hollow flange end (8) by forging and machining techniques;
- joining together said hollow half single throws (9a) such a partial hollow journal (3ah) of one hollow half single throw (9a) is joined with the partial hollow journal (3ah) of another hollow half single throw (9a) such that the joined up journals (3ah) form a hollow journal (3h) of full length, and that hollow partial pin (2ah) of one hollow half single throw (9a) is joined with the hollow partial pin (2ah) of another hollow half single throw (9a) to form a hollow pin (2h) of full length;

- joining hollow tail end (7), and hollow flange end (8) to the respective end partial hollow journal (3ah);
- final machining of said joined hollow half single throws (9a) to form said hollow crankshaft (1a).

18. The method of making a hollow crankshaft (1a) as claimed in claim 17, characterized in that said joining of hollow partial pins (2ah) and hollow partial journals (3ah) is performed using an electron beam welding technique.
19. The method of making a hollow crankshaft (1a) as claimed in claim 18, characterized in that said method further comprises the step of forming hollow partial pins (2ah) and hollow partial journals (3ah) prior to the step of joining together said hollow half single throws (9a).
20. The method of making a hollow crankshaft (1a) as claimed in claim 19, characterized in that said method comprises the step of providing oil holes (6) connecting said hollow journal (3h) and said hollow pin (2h) such that the ends of said oil hole (6) open into the hollowed parts of said hollow journal (3h) and said hollow pin (2h).