A crankshaft and an internal combustion engine including variable compression ratio

Abstract

A crankshaft (1, 40) for an internal combustion engine including variable compression ratio comprises a main journal (2, 42) including a crankshaft axis (5, 41), a crankpin (3, 43) including a crankpin axis (7) and a crank web (4, 44) located between the main journal (2, 42) and the crankpin (3, 43) in longitudinal direction of the crankshaft axis (5, 41) and an eccentric member (6, 45) which is mounted on the crankpin (3, 43) and rotatable with respect to the crankpin (3, 43) about the crankpin axis (7). The eccentric member (6, 45) comprises a bearing portion (8, 46) for supporting a big end of a connecting rod. The bearing portion (8, 46) has a centreline extending parallel to the crankpin axis (5, 41). The eccentric member (6, 45) also comprises an external eccentric member gear (10, 48) between the bearing portion (8, 46) and the crank web (4, 44) as seen in longitudinal direction of the crankshaft axis (5, 41. The eccentric member gear (10, 48) is drivably coupled to an external central gear (13, 49) which is fixed to a central shaft (15, 50). The central shaft (15, 50) extends through the main journal (2, 42) and through the crank web (4, 44). The central shaft (15, 50) is rotatable with respect to the main journal (2, 42) and the crank web (4, 44). The central shaft (15, 50) is radially supported by a separate supporting element (26, 53) which is attached to the crank web (4, 44) at a side where the eccentric member (6, 45) is located.

Description

[0001] The present invention relates to a crankshaft for an internal combustion engine including variable compression ratio comprising a main journal including a crankshaft axis, a crankpin including a crankpin axis and a crank web located between the main journal and the crankpin in longitudinal direction of the crankshaft axis, an eccentric member which is mounted on the crankpin and rotatable with respect to the crankpin about the crankpin axis, wherein the eccentric member comprises a bearing portion for supporting a big end of a connecting rod, which bearing portion has a centreline extending parallel to the crankpin axis, and an external eccentric member gear between the bearing portion and the crank web as seen in longitudinal direction of the crankshaft axis, wherein the eccentric member gear is drivably coupled to an external central gear which is fixed to a central shaft, wherein the central shaft extends through the main journal and through the crank web, wherein the central shaft is rotatable with respect to the main journal and the crank web.

[0002] Such a crankshaft is known from EP 2 620 614 of the same applicant. The known crankshaft is suitable for an internal combustion engine and provides the opportunity to vary the compression ratio of the internal combustion engine by turning the eccentric member about the crankpin at a virtual standstill of the crankshaft. Increasing the compression ratio under part-load conditions of the internal combustion engine leads to improved efficiency, i.e. a lower fuel consumption. In order to allow the central shaft to pass through the main journal and through the crank web a central through-hole is drilled in the main journal and through the crank web. In the known crankshaft the central shaft is radially supported within the central through-hole. Since the central gear of the known crankshaft meshes with intermediate gears its position, e.g. its axis of rotation, should be very accurate to minimize noise for example. It appears to be difficult to achieve the desired high level of accuracy in the known crankshaft.

[0003] An object of the invention is to provide a further improved crankshaft.

[0004] This object is accomplished with the crankshaft according to the invention which is characterized in that the central shaft is radially supported by a separate supporting element which is attached to the crank web at a side where the eccentric member is located.

[0005] It appears that the supporting element can be located and attached to the corresponding crank web accurately such that it forms an accurate basis for radially supporting the central shaft. This means that the central shaft of the crankshaft according to the invention is advantageously located and radially supported accurately with respect to the main journal and the crank web.

[0006] The central shaft may extend concentrically through the main journal.

[0007] In a practical embodiment the central shaft is supported by the supporting element through a roller bearing, preferably a needle bearing.

[0008] In a particular embodiment the eccentric member gear is drivably coupled to the central gear through an external intermediate gear which meshes with both the eccentric member gear and the central gear and which is rotatably mounted to at least one of the crank web and the supporting element.

[0009] In an embodiment the intermediate gear is rotatably mounted to an intermediate gear shaft, preferably through a roller bearing, wherein the intermediate gear shaft is fixed to at least one of the crank web and the supporting element, wherein preferably the supporting element is positioned to the crank web through the intermediate gear shaft when it is fixed to the crank web and the supporting element. For example, the intermediate gear shaft is fixed in a hole in the crank web and a hole in the supporting element, possibly through press fittings. Positions of such holes can be provided accurately. As a consequence, the positioning of the supporting element is also accurate. Besides, such holes in the crank web and the supporting element can be machined relatively easily.

[0010] In an embodiment an axial end of the central shaft at an end portion of the central shaft where the central shaft is supported by the supporting element is provided with an abutment for preventing the central shaft from a displacement with respect to the main journal in a direction from the supporting element to the main journal, which abutment abuts against the supporting element.

[0011] The abutment may be releasably mounted to the axial end of the central shaft, for example through a bolt. A head of the bolt may abut against the supporting element.

[0012] The supporting element may be attached to the crank web through at least a bolt that passes through a through-hole of the crank web and fits in a threaded hole of the supporting element in a direction from the main journal to the supporting element. This allows the supporting element to be drawn against the crank web upon tightening the bolt.

[0013] The central gear and the supporting element may be adapted such that the supporting element forms an abutment for preventing the central shaft from a displacement with respect to the main journal in a direction from the main journal to the supporting element.

[0014] The central gear may abut against the supporting element such that the supporting element forms the abutment for preventing the central shaft from a displacement with respect to the main journal in a direction from the main journal to the supporting element. In this case the central gear may be located between the main journal and the supporting element as seen along the crankshaft axis.

[0015] In an alternative embodiment the central shaft and the supporting element are adapted such that the supporting element forms an abutment for preventing the central shaft from a displacement with respect to the main journal in a direction from the supporting element to the main journal.

[0016] The central gear may abut against the supporting element such that the supporting element forms the abutment for preventing the central shaft from a displacement with respect to the main journal in a direction from the supporting element to the main journal. In this case the supporting element may be located between the central gear and the main journal as seen along the crankshaft axis.

[0017] In a particular embodiment a cover may be attached to the supporting element at a side where the eccentric member is located, wherein the intermediate gear is rotatably mounted to the supporting element and the cover. The intermediate gear may be rotatably mounted to an intermediate gear shaft which in turn is fixed to the supporting element as well as to the cover, for example through press fittings.

[0018] In an embodiment the central gear and the supporting element are a first central gear and a first supporting element, wherein at an opposite side of the main journal the crankshaft is provided with a similar second supporting element for supporting the central shaft and a second central gear which is fixed to the central shaft, wherein the second central gear abuts against the second supporting element such that the second supporting element forms an abutment for preventing the central shaft from a displacement with respect to the main journal in a direction from the second supporting element to the first supporting element.

[0019] The main journal, the crank web and the crankpin may be made in one piece. The eccentric member may be composed of at least two parts.

[0020] The invention is also related to an internal combustion engine including variable compression ratio, comprising a crankshaft as described hereinbefore and an engine block which supports at least the main journal, wherein the main journal is rotatable with respect to the engine block about the crankshaft axis.

[0021] The invention will hereafter be elucidated with reference to very schematic drawings showing embodiments of the invention by way of example. Fig. 1 is a perspective view of an embodiment of a crankshaft according to the invention. Fig. 2 is a perspective sectional view of the crankshaft as shown in Fig. 1. Fig. 3 is an enlarged view of a part of Fig. 2. Fig. 4 is an enlarged view of a part of Fig. 1. Fig. 5 is a similar view as Fig. 4, showing an opposite side of the part of Fig. 4. Fig. 6 is a similar view as Fig. 1, but showing an alternative embodiment. Fig. 7 is an enlarged exploded view of a part of Fig. 6.

[0022] Figs. 1-3 show an embodiment of a crankshaft 1 for an internal combustion engine including variable compression ratio according to the invention. The crankshaft 1 is suitable for a three-cylinder four-stroke Otto engine. The crankshaft 1 has four main journals 2 which are supported by an engine block (not shown) when the crankshaft 1 is mounted to the engine block, three crankpins 3 and a pair of crank webs 4 at opposite sides of each crankpin 3. Under operating conditions the crankshaft 1 is rotatable with respect to the engine block about a crankshaft axis 5 which forms a centreline through the main journals 2. Each of the crank webs 4 is located between the adjacent main journal 2 and the adjacent crankpin 3 thereof as seen in longitudinal direction of the crankshaft axis 5. The main journals 2, the crank webs 4 and the crankpins 3 are made in one piece. In an alternative embodiment the internal combustion engine may have a different number of cylinders, i.e. the crankshaft 1 may have a different number of main journals 2, crank webs 4 and crankpins 3.

[0023] The crankshaft 1 is provided with three eccentric members 6 which are rotatably mounted on the respective crankpins 3. Each of the eccentric members 6 is rotatable with respect to the corresponding crankpin 3 about a crankpin axis 7 and comprises a bearing portion 8 for supporting a big end of a connecting rod (not shown). The bearing portion 8 of each eccentric member 6 is circular cylindrical and has a centreline parallel to the crankpin axis 7 of the corresponding crankpin 3. Each of the eccentric members 6 has a circular cylindrical inner wall including a centreline which coincides with the crankpin axis 7 of the corresponding crankpin 3. Since the centreline of the bearing portion 8 is parallel to the crankpin axis 7 they extend at a distance from each other. Hence, the bearing portion 8 and the inner wall of each eccentric member 6 are disposed eccentrically with respect to each other.

[0024] For clarity reasons, in Figs. 1 and 2 several parts of the crankshaft 1 are not shown. Since the main journals 2, the crank webs 4 and the crankpins 3 are made in one piece, each of the eccentric members 6 is made of at least two mating pieces in order to enable assembly of the crankshaft 1. Such eccentric members are disclosed in EP 2 873 835 of the same applicant.

[0025] A front end of the crankshaft 1 is provided with a pulley 9 which has a fixed position with respect to the main journals 2. The eccentric member 6 closest to the pulley 9 has an external front eccentric member gear 10 and an external rear eccentric member gear 11. The front eccentric member gear 10 is located between the bearing portion 8 and the crank web 4 closest to the pulley 9 as seen in longitudinal direction of the crankshaft axis 5. The bearing portion 8 lies between the front eccentric member gear 10 and the rear eccentric member gear 11.

[0026] The front eccentric member gear 10 meshes with two external intermediate gears 12, which in turn mesh with an external central gear in the form of an auxiliary gear 13. The front eccentric member gear 10 and the auxiliary gear 13 are located behind each other as seen along the crankshaft axis 5. For this reason, the intermediate gears 12 are wider than each of the front eccentric member gear 10 and the auxiliary gear 13. In an alternative embodiment (not shown) the intermediate gears 12, the auxiliary gear 13 and the front eccentric member gear 10 may lie in a single plane.

[0027] The intermediate gears 12 are rotatably mounted to respective intermediate gear shafts 14, for example through needle bearings. The intermediate gear shafts 14 are fixed to the crank web 4 which is closest to the pulley 9, for example by press fittings in respective holes in the crank web 4. The intermediate gears 12 are rotatable about intermediate gear axes which extend parallel to the crankshaft axis 5. The auxiliary gear 13 is fixed to a central shaft in the form of an auxiliary shaft 15, for example through a press fitting, which auxiliary shaft 15 extends concentrically through a central through-hole through the main journal 2 closest to the pulley 9 and through the adjacent crank web 4. The auxiliary shaft 15 has a centreline that coincides with the crankshaft axis 5 and is rotatable with respect to the main journal 2 about the crankshaft axis 5.

[0028] Inside the circumference of the pulley 9 is a control system 16 for adjusting an angular position of the auxiliary shaft 15 with respect to the engine block in order to vary the compression ratio of the internal combustion engine. In this case the control system 16 comprises a hydraulic actuator 17 which is rotatable within a housing 18. The hydraulic actuator 17 is fixed to the auxiliary shaft 15 and drivable in rotational direction by hydraulic pressure. The housing 18 is located at the front end of the crankshaft 1 and fixed to the engine block in rotational direction about the crankshaft axis 5 through a rod 19, but rotatable with respect to the main journals 2, crankpins 3 and crank webs 4. An alternative control system is conceivable, for example a worm - worm wheel mechanism as disclosed in EP 2 620 614 of the same applicant.

[0029] The front eccentric member gear 10, the intermediate gears 12 and the auxiliary gear 13 are dimensioned such that under operating conditions, in case of a standstill of the auxiliary shaft 15 with respect to the engine block, the corresponding eccentric member 6 is rotated with respect to the corresponding crankpin 3 at half speed of the speed of the crankshaft 1 with respect to the engine block and rotated with respect to the corresponding crankpin 3 in opposite direction of the rotational direction of the crankshaft 1 with respect to the engine block.

[0030] The rear eccentric member gear 11 of the eccentric member 6 closest to the pulley 9 meshes with an external first transfer gear 20 which is fixed to a front end of a first transfer shaft 21. An external second transfer gear 22 is fixed to a rear end of the first transfer shaft 21. The first transfer shaft 21 is mounted inside a second main journal 2 as counted from the pulley 9 and rotatable with respect to that second main journal 2 about the crankshaft axis 5. It is noted that the first transfer shaft 21 extends concentrically through the second main journal 2, but in an alternative embodiment (not shown) it may extend eccentrically through the second main journal 2.

[0031] The second transfer gear 22 meshes with an external front eccentric member gear 23 of the eccentric member 6 which is the middle one of the three eccentric members 6. The front eccentric member gear 23 of the middle one of the eccentric members 6 has the same dimensions as the rear eccentric member gear 11 of the eccentric member 6 closest to the pulley 9. The first and second transfer gears 20, 22 are also the same. This means that under operating conditions the middle one of the eccentric members 6 rotates with respect to its corresponding crankpin 3 in the same direction and at the same speed as the eccentric member 6 closest to the pulley 9 with respect to its corresponding crankpin 3.

[0032] In a similar manner an external rear eccentric member gear 24 of the middle one of the eccentric members 6 is drivably coupled to an external eccentric member gear 25 of the eccentric member 6 which is located furthest away from the pulley 9, see Fig. 2. This means that under operating conditions each of the eccentric members 6 has the same motion with respect to its corresponding crankpin 3. The latter eccentric member 6 has only one eccentric member gear 25 at a side of its bearing portion 8 which is closest to the pulley 9.

[0033] The crankshaft 1 is provided with a separate supporting element 26, which is shown as a separate part in Figs. 4 and 5. The supporting element 26 is attached to the crank web 4 closest to the pulley 9 at a side where the eccentric member 6 closest to the pulley 9 is located. Fig. 4 shows a side of the supporting element 26 which faces the crank web 4. The supporting element 26 is attached to the crank web 4 through bolts 27 which pass through respective through-holes of the crank web 4 and fit in respective threaded holes 28 of the supporting element 26. Fig. 1 shows a head of one of the bolts 27. It can be seen that the bolt 27 is inserted in the crank web 4 and the supporting element 26 in a direction from the pulley 9 to the supporting element 26 such that the supporting element 26 can be pulled against the crank web 4 upon tightening the bolts 27. Figs. 4 and 5 show through-holes 29 in the supporting element 26 in which the respective intermediate gear shafts 14 are fixed through press fittings. The intermediate gear shafts 14 are also fixed in respective holes in the crank web 4 through press fittings, see Fig. 1. In addition to the press fittings the bolts 27 secure the supporting element 26 to the crank web 4. Positions of the through-holes 29 in the supporting element 26 and the holes in the crank web 4 can be provided accurately.

[0034] Fig. 3 shows that an end portion of the auxiliary shaft 15 at a distance from the pulley 9 is radially supported by the supporting element 26 through a needle bearing 30. Furthermore, a portion of the supporting element 26 around the needle bearing 30 forms an abutment 31 against which the auxiliary gear 13 abuts so as to prevent the auxiliary shaft 15 from a displacement with respect to the corresponding main journal 2 in a direction from the pulley 9 to the supporting element 26. The auxiliary shaft 15 is also locked in opposite direction, i.e. in a direction from the supporting element 26 to the pulley 9, by a bolt head 32 of a bolt which is screwed into an axial end of the auxiliary shaft 15. The bolt head 32 contacts a contact surface 33 of the supporting element 26. The needle bearing 30 is surrounded and radially supported by a tubular supporting surface around a through-hole 34 in the supporting element 26, see Figs. 4 and 5.

[0035] As described above the through-holes 29 in the supporting element 26 and the holes in the crank web 4 can be provided accurately, which means that the supporting element 26 can also be positioned to the corresponding crank web 4 accurately through the intermediate gear shafts 14 when they are fixed to the crank web 4 and the supporting element 26. This also means that the auxiliary shaft 15 can be radially supported through the needle bearing 31 accurately, as well. It is difficult to reach a comparable accuracy by radially supporting the auxiliary shaft 15 directly within the main journal 2 and / or the crank web 4 since the accuracy of drilling the central through-holes through all the main journals 2 and the crank webs 4 of the crankshaft 1, in particular for a multi-cylinder engine, is relatively low.

[0036] The auxiliary shaft 15 is also radially supported by an additional needle bearing 35, that supports the hydraulic actuator 17 which in turn is fixed to the auxiliary shaft.

[0037] Fig. 6 shows an alternative embodiment of a crankshaft 40 according to the invention. In this case the crankshaft 40 is suitable for a multi-cylinder four-stroke Diesel engine including variable compression ratio, but could also be applied in an Otto engine. The crankshaft 40 has a crankshaft axis 41. Fig. 6 shows two main journals 42, crankpins 43 and crank webs 44 of the crankshaft 40. Each crank web 44 lies between an adjacent crankpin 43 and an adjacent main journal 42 as seen in longitudinal direction of the crankshaft axis 41.

[0038] Similar to the embodiment as shown in Figs. 1-5 the crankshaft 40 is provided with eccentric members 45, which are rotatably mounted on the respective crankpins 43 and rotatable about respective crankpin axes. Each of the eccentric members 45 is also provided with a bearing portion 46 for supporting a big end of a connecting rod. Similar to the embodiment as shown in Figs. 1-5 the bearing portion 46 of each eccentric member 45 has a centreline parallel to a corresponding crankpin axis. An external rear eccentric member gear 47 of one of the eccentric members 45 is drivably coupled with an external front eccentric member gear 48 of a neighbouring eccentric member 45. The front eccentric member gear 48 is located between the bearing portion 46 of the corresponding eccentric member 45 and the adjacent crank web 44 as seen in longitudinal direction of the crankshaft axis 41.

[0039] The front eccentric member gear 48 is drivably coupled to an external first central gear in the form a first transfer gear 49 through two external intermediate transfer gears 51. The first transfer gear 49 is fixed to a first end of a central shaft in the form of a transfer shaft 50 through a bolt 61. In order to fix the first transfer gear 49 to the transfer shaft 50 appropriately, the first transfer gear 49 and the transfer shaft 50 may be provided with mating splines. Each of the intermediate transfer gears 51 meshes with the first transfer gear 49 and the front eccentric member gear 48. The widths of the intermediate transfer gears 51 are larger than the width of the front eccentric member gear 48 and larger than the width of the first transfer gear 49. The transfer shaft 50 extends concentrically through the central through-hole in one of the main journals 42 and the crank webs 44 at opposite sides of that main journal 43. The transfer shaft 50 is rotatable with respect to the corresponding main journal 42 and crank webs 44.

[0040] In a similar way the rear eccentric member gear 47 is drivably coupled to an external second central gear in the form of a second transfer gear 52 through two external intermediate transfer gears. The second transfer gear 52 is fixed to a second end of the transfer shaft 50 through a bolt 61. This configuration urges the eccentric members 45 to rotate in the same direction and at the same speed about the respective crankpins 43. It is noted that, in contrary to the embodiment as shown in Figs. 1-5, the rear eccentric member gear 47 does not directly engage the second transfer gear 52 and the front eccentric member gear 48 does not directly engage the first transfer gear 49. This is caused by the relatively large diameters of the front and rear eccentric member gears 47, 48.

[0041] The transfer shaft 50 is radially supported by separate supporting elements 53 which are attached to the respective crank webs 44 at sides where the respective adjacent eccentric members 45 are located. One of the separate supporting elements 53 is shown in Fig. 7. Each supporting element 53 has a sleeve 54 in which a needle bearing 55 is provided through a press fitting. The transfer shaft 50 fits in inner sides of the respective needle bearings 55. The sleeve 54 fits in a central through-hole through the corresponding main journal 42 and crank webs 44 with play. An oil guide tube 56 is located between the needle bearings 55 of the transfer shaft 50 in order to guide lubricant from an inner side of the main journal 42 to the eccentric member 45.

[0042] The crankshaft 40 is provided with covers 57 which can be fixed to the respective supporting elements 53 and crank webs 44 through bolts 58. Each of the bolts 58 can be successively inserted into through-holes in the crank web 44 and the supporting element 53 and screwed into a threaded hole 59 in the cover 57 such that the supporting element 53 is clamped between the crank web 44 and the cover 57. The intermediate transfer gears 51 are located between the supporting element 53 and the cover 57. Each of the intermediate transfer gears 51 is rotatably mounted on an intermediate gear shaft 60 which in turn is fixed in both the supporting element 53 and the cover 57, for example through press fittings.

[0043] The transfer shaft 50 is locked with respect to the corresponding main journal 42 in a direction along the crankshaft axis 41 through the first and second transfer gears 49, 52 which abut against the respective supporting elements 53.

[0044] It is noted that the supporting element 26 in the embodiment as shown in Figs. 1-5 radially supports the auxiliary shaft 15 whereas the supporting elements 53 in the embodiment as shown in Figs. 6 and 7 radially support the transfer shaft 50, but the principle for radially supporting the auxiliary shaft 15 and the transfer shaft 50 by a separate supporting element 26, 53 is similar.

[0045] The invention is not limited to the embodiments shown in the drawings and described hereinbefore, which may be varied in different manners within the scope of the claims and their technical equivalents.

Claims

1. A crankshaft (1, 40) for an internal combustion engine including variable compression ratio comprising a main journal (2, 42) including a crankshaft axis (5, 41), a crankpin (3, 43) including a crankpin axis (7) and a crank web (4, 44) located between the main journal (2, 42) and the crankpin (3, 43) in longitudinal direction of the crankshaft axis (5, 41), an eccentric member (6, 45) which is mounted on the crankpin (3, 43) and rotatable with respect to the crankpin (3, 43) about the crankpin axis (7), wherein the eccentric member (6, 45) comprises a bearing portion (8, 46) for supporting a big end of a connecting rod, which bearing portion (8, 46) has a centreline extending parallel to the crankpin axis (5, 41), and an external eccentric member gear (10, 48) between the bearing portion (8, 46) and the crank web (4, 44) as seen in longitudinal direction of the crankshaft axis (5, 41), wherein the eccentric member gear (10, 48) is drivably coupled to an external central gear (13, 49) which is fixed to a central shaft (15, 50), wherein the central shaft (15, 50) extends through the main journal (2, 42) and through the crank web (4, 44), wherein the central shaft (15, 50) is rotatable with respect to the main journal (2, 42) and the crank web (4, 44), characterized in that the central shaft (15, 50) is radially supported by a separate supporting element (26, 53) which is attached to the crank web (4, 44) at a side where the eccentric member (6, 45) is located.

2. A crankshaft (1, 40) according to claim 1, wherein the central shaft (15, 50) is supported by the supporting element (26, 53) through a roller bearing, preferably a needle bearing (30, 55).

3. A crankshaft (1, 40) according to claim 1 or 2, wherein the eccentric member gear (10, 48) is drivably coupled to the central gear (13, 49) through an external intermediate gear (12, 51) which meshes with both the eccentric member gear (10, 48) and the central gear (13, 49) and which is rotatably mounted to at least one of the crank web (4, 44) and the supporting element (26, 53).

4. A crankshaft (1, 40) according to claim 3, wherein the intermediate gear (12, 51) is rotatably mounted to an intermediate gear shaft (14, 60), preferably through a roller bearing, wherein the intermediate gear shaft (14, 60) is fixed to at least one of the crank web (4, 44) and the supporting element (26, 53), wherein preferably the supporting element (26, 53) is positioned to the crank web (4, 44) through the intermediate gear shaft (14, 60) when it is fixed to the crank web (4, 44) and the supporting element (26, 53).

5. A crankshaft (1) according to any one of the preceding claims, wherein an axial end of the central shaft (15, 50) at an end portion of the central shaft (15, 50) where the central shaft (15, 50) is supported by the supporting element (26, 53) is provided with an abutment (32, 49) for preventing the central shaft (15, 50) from a displacement with respect to the main journal (2, 42) in a direction from the supporting element (26, 53) to the main journal (2, 42), which abutment (32, 49) abuts against the supporting element (26, 53).

6. A crankshaft (1) according to claim 5, wherein the abutment is releasably mounted to the axial end of the central shaft (15, 50), for example through a bolt (32, 61).

7. A crankshaft (1) according to any one of the preceding claims, wherein the supporting element (26) is attached to the crank web (4) through at least a bolt (27) that passes through a through-hole of the crank web (4) and fits in a threaded hole (28) of the supporting element (26) in a direction from the main journal (2) to the supporting element (26).

8. A crankshaft (1) according to any one of the preceding claims, wherein the central gear (13) and the supporting element (26) are adapted such that the supporting element (26) forms an abutment for preventing the central shaft (15) from a displacement with respect to the main journal (2) in a direction from the main journal (2) to the supporting element (26) .

9. A crankshaft (1) according to claim 8, wherein the central gear (13) abuts against the supporting element (26) such that the supporting element (26) forms the abutment for preventing the central shaft (15) from a displacement with respect to the main journal (2) in a direction from the main journal (2) to the supporting element (26).

10. A crankshaft (40) according to any one of the claims 1-4, wherein the central shaft (50) and the supporting element (53) are adapted such that the supporting element (53) forms an abutment for preventing the central shaft (50) from a displacement with respect to the main journal (42) in a direction from the supporting element (53) to the main journal (2) .

11. A crankshaft (40) according to claim 10, wherein the central gear (49) abuts against the supporting element (53) such that the supporting element (53) forms the abutment for preventing the central shaft (50) from a displacement with respect to the main journal (42) in a direction from the supporting element (53) to the main journal (42).

12. A crankshaft (40) according to claim 11 depending on claim 3, wherein a cover (57) is attached to the supporting element (53) at a side where the eccentric member (45) is located, wherein the intermediate gear (51) is rotatably mounted to the supporting element (53) and the cover (57).

13. A crankshaft (40) according to any one of the claims 10-12, wherein the central gear and the supporting element are a first central gear (49) and a first supporting element (53), wherein at an opposite side of the main journal (42) the crankshaft (40) is provided with a similar second supporting element (53) for supporting the central shaft (50) and a second central gear (52) which is fixed to the central shaft (50), wherein the second central gear (52) abuts against the second supporting element (53) such that the second supporting element (53) forms an abutment for preventing the central shaft (50) from a displacement with respect to the main journal (42) in a direction from the second supporting element (53) to the first supporting element (53).

14. A crankshaft (1, 40) according to any one of the preceding claims, wherein the main journal (2, 42), the crank web (4, 44) and the crankpin (3, 43) are made in one piece.

15. An internal combustion engine including variable compression ratio, comprising a crankshaft (1, 40) according to any one of the preceding claims and an engine block which supports at least the main journal (2, 42), wherein the main journal (2, 42) is rotatable with respect to the engine block about the crankshaft axis (5, 41).

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