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, a first crankpin (3a, 43a), a first and second crank web (4a, 4b, 44a, 44b) at opposite sides of the first crankpin (3a, 43a), a second crankpin (3b, 43b) and a third and fourth crank web (4c, 4d, 44c, 44d) at opposite sides of the second crankpin (3b, 43b). The crankshaft also includes a first eccentric member (6a, 45a) which is rotatably mounted on the first crankpin (3a, 43a) and a second eccentric member (6b, 45b) which is rotatably mounted on the second crankpin (3b, 43b) and a transfer shaft (19, 50) which extends through the second and third crank web (4b, 4c, 44b, 44c) and which is rotatable with respect to the second and third crank web (4b, 4c, 44b, 44c) about a transfer shaft axis. An external first transfer gear (18, 52) is fixed to the transfer shaft (19, 50) at a side of the second crank web (4b, 44b) where the first eccentric member (6a, 45a) is located and an external second transfer gear (21, 49) is fixed to the transfer shaft (19, 50) at a side of the third crank web (21, 44c) where the second eccentric member (6b, 45b) is located. The first and second eccentric members (6a, 6b, 45a, 45b) are drivably coupled to each other through the transfer shaft (19, 50). The first and second transfer gears (18, 21, 47, 48) mesh with external first and second intermediate transfer gears (17, 22, 51), respectively, which in turn mesh with the first and second eccentric member gears (10, 23, 47, 48). The first and second intermediate transfer gears (17, 22, 51) are rotatably mounted to the second and third crank webs (4b, 4c, 44b, 44c), respectively

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 first crankpin, a first and second crank web at opposite sides of the first crankpin, a second crankpin, a third and fourth crank web at opposite sides of the second crankpin, wherein the second and third crank web are adjacent to each other and the first crank web is adjacent to the main journal, a first eccentric member which is rotatably mounted on the first crankpin and which comprises a first bearing portion for supporting a big end of a connecting rod and an external first eccentric member gear located between the first bearing portion and the second crank web, a second eccentric member which is rotatably mounted on the second crankpin and which comprises a second bearing portion for supporting a big end of a connecting rod and an external second eccentric member gear located between the second bearing portion and the third crank web, a transfer shaft which extends through the second and third crank web and which is rotatable with respect to the second and third crank web about a transfer shaft axis, wherein an external first transfer gear is fixed to the transfer shaft at a side of the second crank web where the first eccentric member is located and an external second transfer gear is fixed to the transfer shaft at a side of the third crank web where the second eccentric member is located, wherein the first and second eccentric members are drivably coupled to each other through the transfer shaft such that rotation of the first eccentric member about the first crankpin causes the second eccentric member to rotate about the second crankpin by the same angle and in the same direction.

[0002] Such a crankshaft is known from EP 2 620 614 of the same applicant. The known crankshaft is applied in an internal combustion engine and provides the opportunity to vary the compression ratio of the internal combustion engine by turning the first and second eccentric members 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.

[0003] In the known internal combustion engine the first eccentric member has an external main eccentric member gear which is located between the first bearing portion and the first crank web, whereas the main eccentric member gear meshes with a main intermediate gear which in turn meshes with an auxiliary gear. The auxiliary gear is fixed to an auxiliary shaft which in turn extends through the first crank web and the main journal. The auxiliary shaft is rotatable with respect to the main journal and the first crank web. The main intermediate gear is rotatably mounted to the first crank web at a side of the first crank web where the first eccentric member is located.

[0004] Furthermore, the first eccentric member gear meshes with the first transfer gear and the second eccentric member gear meshes with the second transfer gear such that under operating conditions the first and second eccentric members have the same motions about the first and second crankpins, respectively. In the event that the first and second crankpins have relatively large diameters, for example in case of a Diesel engine, the first and second transfer gears may become relatively small, which might lead to overloading the first and second transfer gears.

[0005] An object of the invention is to provide an improved crankshaft.

[0006] This object is accomplished with the crankshaft according to the invention which is characterized in that the first and second transfer gears mesh with external first and second intermediate transfer gears, respectively, which in turn mesh with the first and second eccentric member gears, wherein the first and second intermediate transfer gears are rotatably mounted to the second and third crank webs, respectively.

[0007] The crankshaft according to the invention provides the opportunity to lower the tooth forces on the first and second transfer gears. For example, it is possible to apply more than one first intermediate transfer gear and / or more than one second intermediate transfer gear such that the first transfer gear meshes with a plurality of first intermediate transfer gears and / or the second transfer gear meshes with a plurality of second intermediate transfer gears in order to distribute forces over different teeth of the first and / or second transfer gear. The crankshaft according to the invention also provides the opportunity to arrange the first transfer gear and the first eccentric member gear next to each other as seen in longitudinal direction of the crankshaft axis and / or to arrange the second transfer gear and the second eccentric member gear next to each other as seen in longitudinal direction of the crankshaft axis. This allows to apply a relatively large first transfer gear and / or second transfer gear, respectively.

[0008] In an embodiment the second and third crank webs are interconnected through a further main journal, wherein the transfer shaft also extends through the further main journal. This provides the opportunity to support the crankshaft between the first and second crankpins when mounted in an engine block.

[0009] The transfer shaft axis may coincide with the crankshaft axis. This is advantageous in terms of manufacturing the crankshaft.

[0010] In a preferred embodiment the first and second transfer gears are identical and / or the first and second intermediate transfer gears are identical and / or the first and second eccentric member gears are identical, since this provides the opportunity to manufacture the crankshaft efficiently.

[0011] It is essential that the dimensions of the first and second transfer gears and the first and second eccentric member gears are selected such that the first and second eccentric members have the same motions about the first and second crankpins, respectively, under operating conditions in an internal combustion engine. The dimensions of the first and second intermediate transfer gears do not influence these motions; it is even possible, for example, that the first and second transfer gears are identical and the first and second eccentric member gears are identical, whereas the first and second intermediate transfer gears are different.

[0012] In an embodiment the first intermediate transfer gear is one of two first intermediate transfer gears which mesh with both the first eccentric member gear and the first transfer gear, wherein both first intermediate transfer gears are rotatably mounted to the second crank web, and / or wherein the second intermediate transfer gear is one of two second intermediate transfer gears which mesh with both the second eccentric member gear and the second transfer gear, wherein both second intermediate transfer gears are rotatably mounted to the third crank web. This embodiment minimizes the risk of overloading teeth of the first and / or second transfer gears. It is noted that the dimensions of the two first intermediate transfer gears may be different and / or the dimensions of the two second intermediate transfer gears may be different.

[0013] In an embodiment the first eccentric member has an external main eccentric member gear which is located between the first bearing portion and the first crank web, wherein the main eccentric member gear is drivably coupled to an auxiliary gear through an external main intermediate gear, which auxiliary gear is fixed to an auxiliary shaft which in turn extends through the first crank web and the main journal and which is rotatable with respect to the main journal and the first crank web, wherein the main intermediate gear is rotatably mounted to the first crank web at a side of the first crank web where the first eccentric member is located. Turning the auxiliary shaft with respect to the main journal and the first crank web forces the first and second eccentric members to rotate by the same angle about the first crankpin and the second crankpin, respectively, and in the same rotational direction.

[0014] In a particular embodiment the first intermediate transfer gear is mounted to a first intermediate transfer gear shaft that is radially supported by both the second crank web and a separate supporting element, which is attached to the second crank web at a circumferential side thereof or by a separate supporting element, which is attached to the second crank web at a side where the first eccentric member is located or at a circumferential side thereof and / or wherein the second intermediate transfer gear is mounted to a second intermediate transfer gear shaft that is radially supported by both the third crank web and a separate supporting element, which is attached to the third crank web at a circumferential side thereof or by a separate supporting element, which is attached to the third crank web at a side where the second eccentric member is located or at a circumferential side thereof.

[0015] In an embodiment the first crankpin includes a first crankpin axis and the second crankpin includes a second crankpin axis, wherein the first intermediate transfer gear is one of two first intermediate transfer gears which mesh with both the first eccentric member gear and the first transfer gear, wherein both first intermediate transfer gears are rotatably mounted to the second crank web, wherein the second intermediate transfer gear is one of two second intermediate transfer gears which mesh with both the second eccentric member gear and the second transfer gear, wherein both second intermediate transfer gears are rotatably mounted to the third crank web, wherein the first and second transfer gears are the same and the first and second eccentric member gears are the same, wherein the first and second intermediate transfer gears are dimensioned and positioned such that the transfer shaft axis intersects an adjusting line which is perpendicular to a reference plane that is spanned by the first and second crankpin axes and which adjusting line intersects the crankshaft axis. This allows appropriate meshing between the mentioned gears. In certain cases the first and second intermediate transfer gears are dimensioned and positioned such that the transfer shaft axis does not coincide with the crankshaft axis, but extends parallel to the crankshaft axis.

[0016] 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 the crankshaft as shown in Fig. 2. Fig. 4 is a cross-sectional view of the crankshaft as shown in Fig. 1. Fig. 5 is an enlarged perspective view of an eccentric member of the crankshaft as shown in Figs. 1-4. Fig. 6 is a similar view as Fig. 3, but showing an alternative embodiment of the crankshaft according to the invention. Fig. 7 is an enlarged exploded view of a part of the crankshaft as shown in Fig. 6. Figs. 1-4 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 six-cylinder in-line four-stroke Diesel engine, but is also suitable for an Otto engine. The right side of the crankshaft 1 in Fig. 1 and the left side of the crankshaft 1 in Figs. 2 and 3 5 are defined as a front end of the crankshaft 1, whereas the left side of the crankshaft 1 in Fig. 1 and the right side of the crankshaft 1 in Figs. 2 and 4 are defined as a rear end of the crankshaft 1.

[0017] The crankshaft 1 has seven main journals which are supported by an engine block (not shown) when the crankshaft 1 is mounted to the engine block of an internal combustion engine. A first main journal 2a and a second main journal 2b of the seven main journals are indicated in Figs. 1-3. Furthermore, the crankshaft 1 comprises six crankpins and six pairs of crank webs at opposite sides of the respective crankpins. A first crankpin 3a and a second crankpin 3b of the six crankpins are indicated in Figs. 2 and 3. A first crank web 4a, a second crank web 4b, a third crank web 4c and a fourth crank web 4d of the crank webs are indicated in Figs. 1-3.

[0018] The first crank web 4a and the second crank web 4b are located at opposite sides of the first crankpin 3a as seen in longitudinal direction of the crankshaft axis 5. The third crank web 4c and the fourth crank web 4d are located at opposite sides of the second crankpin 3b as seen in longitudinal direction of the crankshaft axis 5. The second crank web 4b and the third crank web 4c are adjacent to each other. In this case the second crank web 4b and the third crank web 4c are interconnected through the second main journal 2b. The first crank web 4a is adjacent to the first main journal 2a.

[0019] When mounted in an internal combustion engine the crankshaft 1 is rotatable with respect to the engine block about a crankshaft axis 5 which forms a centreline through the main journals. The main journals, the crank webs and the crankpins are made in one piece. In an alternative embodiment the crankshaft may have a different number of main journals, crankpins and crank webs for an internal combustion engine including a different number of cylinders.

[0020] The crankshaft 1 is provided with six eccentric members which are rotatably mounted on the respective crankpins. A first eccentric member 6a and a second eccentric member 6b of the eccentric members are indicated in Figs. 1-3. The first eccentric member 6a is shown as a separate part in Fig. 5. Since the main journals, the crank webs and the crankpins are made in one piece, each of the eccentric members 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.

[0021] The first eccentric member 6a is closest to the front end of the crankshaft 1. The first eccentric member 6a is rotatably mounted on the first crankpin 3a and rotatable about a first crankpin axis 7, see Fig. 3, and comprises a first bearing portion 8a for supporting a big end of a connecting rod (not shown). The first bearing portion 8a is circular cylindrical and has a centreline parallel to the first crankpin axis 7 of the first crankpin 3a. The first eccentric member 6a has a circular cylindrical inner wall including a centreline which coincides with the first crankpin axis 7 of the first crankpin 3a. Since the centreline of the first bearing portion 8a is parallel to the first crankpin axis 7 they extend at a distance from each other. Hence, the first bearing portion 8a and the inner wall of the first eccentric member 6a are disposed eccentrically with respect to each other.

[0022] Similarly, the second eccentric member 6b is rotatably mounted on the second crankpin 3b and rotatable about a second crankpin axis of the second crankpin 3b and comprises a second bearing portion 8b for supporting a big end of a connecting rod (not shown). The second bearing portion 8b is circular cylindrical and has a centreline parallel to the second crankpin axis of the second crankpin 3b. The second eccentric member 6b has a circular cylindrical inner wall including a centreline which coincides with the second crankpin axis of the second crankpin 3b. Since the centreline of the second bearing portion 8b is parallel to the second crankpin axis they extend at a distance from each other. Hence, the second bearing portion 8b and the inner wall of the second eccentric member 6b are disposed eccentrically with respect to each other. The remaining eccentric members are identical to the second eccentric member 3b.

[0023] For clarity reasons, in Figs. 2 and 3 several parts of the crankshaft 1 are not shown.

[0024] The first eccentric member 6a has an external main eccentric member gear 9 and an external first eccentric member gear 10. The main eccentric member gear 9 is located between the first bearing portion 8a and the first crank web 4a as seen in longitudinal direction of the crankshaft axis 5. The first eccentric member gear 10 is located between the first bearing portion 8a and the second crank web 4b as seen in longitudinal direction of the crankshaft axis 5. The first bearing portion 8a lies between the main eccentric member gear 9 and the first eccentric member gear 10.

[0025] The main eccentric member gear 9 meshes with two external main intermediate gears 11, which in turn mesh with an auxiliary gear 12. The main eccentric member gear 9 and the auxiliary gear 12 are located behind each other as seen along the crankshaft axis 5. For this reason, the main intermediate gears 11 are wider than each of the main eccentric member gear 9 and the auxiliary gear 12. In an alternative embodiment (not shown) the main intermediate gears 11, the auxiliary gear 12 and the main eccentric member gear 9 may lie in a single plane.

[0026] The main intermediate gears 11 are rotatably mounted to respective main intermediate gear shafts 13, see Fig. 1, for example through needle bearings. The main intermediate gears 11 are rotatable with respect to the respective main intermediate gear shafts 13 about main intermediate gear axes which extend parallel to the crankshaft axis 5. The main intermediate gear shafts 13 are fixed to the first crank web 4a.

[0027] Fig. 3 shows that the auxiliary gear 12 is fixed to an auxiliary shaft 14 through a bolt 15. The auxiliary gear 12 may be locked to the auxiliary shaft 14 in rotational direction thereof through splines but alternative means are conceivable. The auxiliary shaft 14 extends concentrically through a central through-hole through the first main journal 2a and through the adjacent first crank web 4a thereof. The auxiliary shaft 14 has a centreline that coincides with the crankshaft axis 5 and is rotatable with respect to the corresponding first main journal 2 about the crankshaft axis 5.

[0028] When the crankshaft 1 is applied in an internal combustion engine the angular position of the auxiliary shaft 14 can be adjusted with respect to the engine block in order to vary the compression ratio of the internal combustion engine, for example through a hydraulic control system or a worm - worm wheel mechanism as disclosed in EP 2 620 614 of the same applicant.

[0029] The main eccentric member gear 9 and the auxiliary gear 12 are dimensioned such that under operating conditions, in case of a standstill of the auxiliary shaft 14 with respect to the engine block, the first eccentric member 6a is rotated with respect to the first crankpin 3a at half speed of the speed of the crankshaft 1 with respect to the engine block and is rotated with respect to the first crankpin 3 in opposite direction of the rotational direction of the crankshaft 1 with respect to the engine block. For this reason the gear ratio between the main eccentric member gear 9 and the auxiliary gear 12 equals two.

[0030] Each of the main intermediate gear shafts 13 is radially supported by both the corresponding crank web 4 and a separate supporting element 16, see Fig. 1. Each of the supporting elements 16 is provided with a semi-circular cylindrical recess and the first crank web 4a is provided with two semi-circular cylindrical recesses in which the respective main intermediate gear shafts 13 are accommodated. The supporting elements 16 are located at opposite sides of the first crank web 4a at a circumferential side thereof. They are fixed to the first crank web 4a through bolts. Each of the main intermediate gear shafts 13 is fixed to the first crank web 4a and supporting element 16 by a clamping force between the crank web 4 and the supporting element 16.

[0031] In an alternative embodiment (not shown) the main intermediate gears 11 may be fixed to the main intermediate gear shafts 13, which in turn are rotatable with respect to the first crank web 4a and the supporting elements 16. In the embodiment as shown in Figs. 1-4 the main intermediate gears 11 as well as the supporting elements 16 are mirror symmetrical with respect to a plane which is spanned by the crankshaft axis 5 and the first crankpin axis 7, but this may be different in an alternative embodiment.

[0032] Fig. 4 shows a cross-section of the crankshaft 1 at the first bearing portion 8a of the first eccentric member 6a. It can be seen that the first eccentric member gear 10 of the first eccentric member 6a meshes with two external first intermediate transfer gears 17 which in turn mesh with an external first transfer gear 18. The first eccentric member gear 10 and the first transfer gear 18 are located behind each other as seen along the crankshaft axis 5. For this reason, the first intermediate transfer gears 17 are wider than each of the first eccentric member gear 10 and the first transfer gear 18. In an alternative embodiment (not shown) the first intermediate transfer gears 17, the first transfer gear 18 and the first eccentric member gear 10 may lie in a single plane.

[0033] The first intermediate transfer gears 17 are rotatably mounted to respective first intermediate transfer gear shafts 13', for example through needle bearings. The first intermediate transfer gear shafts 13' are mounted to the second crank web 4b by clamping them between the second crank web 4b and respective separate supporting elements 16' in a similar manner as the main intermediate gear shafts 13 through their corresponding supporting elements 16. The first transfer gear 18 is fixed to a first end of a transfer shaft 19 through a bolt 20, see Fig. 3. An external second transfer gear 21 is fixed to a second end of the transfer shaft 19 through a bolt 20', as well. The first and second transfer gears 18, 21 may be locked to the transfer shaft 19 in rotational direction thereof through splines, but alternative means are conceivable. The transfer shaft 19 is mounted inside the second main journal 2b, the second crank web 4b and the third crank web 4c and rotatable with respect thereto about the crankshaft axis 5.

[0034] The second transfer gear 21 meshes with two external second intermediate transfer gears 22 which in turn mesh with an external second eccentric member gear 23 of the second eccentric member 6b. The second eccentric member gear 23 of the second eccentric member 6b has the same dimensions as the first eccentric member gear 10 of the first eccentric member 6a. The first and second transfer gears 18, 21 are also the same, and the first and second intermediate transfer gears 17, 22 are also the same. This means that the second eccentric member 6b rotates with respect to the second crankpin 3b in the same direction and at the same speed as the first eccentric member 6a with respect to the first crankpin 3a, under operating conditions when the crankshaft 1 is mounted in an internal combustion engine. The mentioned gears may also be different as long as the first and second eccentric members 6a, 6b have the same motions about the first and second crankpins 3a, 3b, respectively, under operating conditions.

[0035] The second intermediate transfer gears 22 are rotatably mounted to respective second intermediate transfer gear shafts 13". The second intermediate transfer gear shafts 13'' are clamped between the third crank web 4c and respective separate supporting elements 16'' in a similar manner as the main intermediate shafts 13 through their corresponding supporting elements 16.

[0036] The remaining eccentric members of the crankshaft 1 are drivably coupled to each other and to the second eccentric member 6b in a similar way as the second eccentric member 6b to the first eccentric member 6a through further transfer shafts, transfer gears, intermediate transfer gears and supporting elements such that all eccentric members have the same motions about the respective crankpins.

[0037] In the embodiment as shown in Figs. 1-5 all eccentric members are identical. The main eccentric member gear 9, the first eccentric member gear 10 and the second eccentric member gear 23 have 60 teeth each. The auxiliary gear 12, the first transfer gear 18 and the second transfer gear 21 have 30 teeth each. The gear ratio of two between the main eccentric member gear 9 and the auxiliary gear 12 is essential for the motion of the first eccentric member 6a under operating conditions. However, the gear ratios between the first eccentric member gear 10 and the first transfer gear 18 as well as the second eccentric member gear 23 and the second transfer gear 21 may be different as long as the second eccentric member 6b has the same motion about the second crankpin 3b as the first eccentric member 6a about the first crankpin 3a under operating conditions. It is even possible that the transfer shaft 19 extends eccentrically through the second main journal 2b.

[0038] Fig. 6 shows a part of an alternative embodiment of a crankshaft 40 according to the invention. In this case the crankshaft 40 is suitable for a multi-cylinder 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 a first main journal 42a and a second main journal 42b, a first crankpin 43a and a second crankpin 43b. The crankshaft 40 has a first crank web 44a, a second crank web 44b, a third crank web 44c and a fourth crank web 44d. The first crank pin 43a lies between the first and second crank webs 44a, 44b, whereas the second crank pin 43b lies between the third and fourth crank webs 44c, 44d as seen in longitudinal direction of the crankshaft axis 41. The second and third crank webs 44b, 44c are interconnected through the second main journal 42b.

[0039] The crankshaft 40 is provided with a first eccentric member 45a and a second eccentric member 45b. The first and second eccentric members 45a, 45b are rotatably mounted on the first and second crankpins 43a, 43b, respectively, and rotatable about respective first and second crankpin axes. The first and second eccentric members 45a, 45b are also provided with first and second bearing portions 46a, 46b for supporting big ends of respective connecting rods. Similar to the embodiment as shown in Figs. 1-5 the first and second bearing portions 46a, 46b have centrelines parallel to the first and second crankpin axes, respectively.

[0040] An external first eccentric member gear 47 of the first eccentric member 45a is drivably coupled to an external second eccentric member gear 48 of the second eccentric member 45b. The first eccentric member gear 47 is located between the first bearing portion 46a and the second crank web 44b as seen in longitudinal direction of the crankshaft axis 41. The second eccentric member gear 48 is located between the second bearing portion 46b and the third crank web 44c as seen in longitudinal direction of the crankshaft axis 41.

[0041] The first eccentric member gear 47 is drivably coupled to an external first transfer gear 52 through two external first intermediate transfer gears (not visible in Fig. 6). Each of the first intermediate transfer gears meshes with both the first transfer gear 52 and the first eccentric member gear 47. The first transfer gear 52 is fixed to a first end of a transfer shaft 50 through a bolt 61. In order to fix the first transfer gear 52 to the transfer shaft 50 appropriately, the first transfer gear 52 and the transfer shaft 50 may be provided with mating splines. The width of each of the first intermediate transfer gears is larger than the width of the first eccentric member gear 47 and larger than the width of the first transfer gear 52.

[0042] The transfer shaft 50 extends concentrically through a central through-hole in the second main journal 42b and the second and third crank webs 44b, 44c at opposite sides of the second main journal 42b. The transfer shaft 50 is rotatable with respect to the second main journal 42b and the second and third crank webs 44b, 44c. In an alternative embodiment (not shown) the transfer shaft 50 may extend eccentrically with respect to the crankshaft axis 41.

[0043] Similar to the embodiment as shown in Figs. 1-5 it is relevant that the first and second crank members 45a, 45b have the same motions about the first and second crankpins 43a, 43b, respectively, under operating conditions when the crankshaft 40 is mounted in an internal combustion engine. In this case the second eccentric member gear 48 is drivably coupled to an external second transfer gear 49 through two external second intermediate transfer gears 51. The second transfer gear 49 is fixed to a second end of the transfer shaft 50 through a bolt 61. The first eccentric member gear 47, the first intermediate transfer gears and the first transfer gear 52 have the same dimensions as the second eccentric member gear 48, the second intermediate transfer gears 51 and the second transfer gear 49, respectively. This configuration urges the first and second eccentric members 45a, 45b to rotate in the same direction and at the same speed about the first and second crankpins 43a, 43b, respectively.

[0044] The transfer shaft 50 is radially supported by separate supporting elements 53 which are attached to the second and third crank webs 44b, 44c at sides where the first and second eccentric members 45a, 45b are located, respectively. One of the separate supporting elements 53 which is attached to the third crank web 44c is shown in Fig. 7. The supporting element 53 which is attached to the second crank web 44b is the same. Referring to Fig. 7 the supporting element 53 has a sleeve 54 in which a needle bearing 55 is provided, for example through a press fitting. The transfer shaft 50 fits in the inner side of the needle bearing 55. The sleeve 54 fits with play in the central through-hole through the second main journal 42b and the second and third crank webs 44b, 44c. 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 second main journal 42b to the first and second eccentric members 45a, 45b.

[0045] The crankshaft 40 is provided with covers 57 which can be fixed to the respective supporting elements 53 and the second and third crank webs 44b, 44c through bolts 58. Referring to Figs. 6 and 7, each of the bolts 58 can be successively inserted into respective through-holes in the second and third crank webs 44b, 44c and the supporting elements 53 and screwed into corresponding threaded holes 59 in the covers 57 such that the supporting elements 53 are clamped between the second and third crank webs 44b, 44c and the covers 57.

[0046] Fig. 7 shows that the second intermediate transfer gears 51 are located between the supporting element 53 and the cover 57. Each of the second intermediate transfer gears 51 is rotatably mounted on a second intermediate transfer gear shaft 60, for example through needle bearings, which second intermediate transfer gear shaft 60 is fixed in both the supporting element 53 and the cover 57, for example through press fittings.

[0047] The transfer shaft 50 is locked with respect to the second main journal 42b 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.

[0048] It is noted that the transfer shaft 50 is not necessarily supported by the supporting elements 53. This means that the supporting elements 53 may be applied for supporting the first and second intermediate transfer gears 51, whereas the transfer shaft 50 may be supported by the second main journal 42b and the second and third crank webs 44.

[0049] The invention is also related to the following aspect: A crankshaft for an internal combustion engine including variable compression ratio comprising a main journal including a crankshaft axis, a first crankpin including a first crankpin axis, a first and second crank web at opposite sides of the first crankpin, a second crankpin including a second crankpin axis, a third and fourth crank web at opposite sides of the second crankpin, wherein the second and third crank web are adjacent to each other and the first crank web is adjacent to the main journal, a first eccentric member which is rotatably mounted on the first crankpin and which comprises a first bearing portion for supporting a big end of a connecting rod and an external first eccentric member gear located between the first bearing portion and the second crank web, a second eccentric member which is rotatably mounted on the second crankpin and which comprises a second bearing portion for supporting a big end of a connecting rod and an external second eccentric member gear located between the second bearing portion and the third crank web, a transfer shaft which extends through the second and third crank web and which is rotatable with respect to the second and third crank web about a transfer shaft axis, wherein an external first transfer gear is fixed to the transfer shaft at a side of the second crank web where the first eccentric member is located and an external second transfer gear is fixed to the transfer shaft at a side of the third crank web where the second eccentric member is located, wherein the first and second eccentric members are drivably coupled to each other through the transfer shaft such that rotation of the first eccentric member about the first crankpin causes the second eccentric member to rotate about the second crankpin by the same angle and in the same direction, wherein the first transfer gear meshes with two external first intermediate transfer gears which in turn mesh with the first eccentric member gear, wherein the second transfer gear meshes with two external second intermediate transfer gears, which in turn mesh with the second eccentric member gear, wherein the first and second transfer gears are the same and the first and second eccentric member gears are the same, wherein the first and second intermediate transfer gears are dimensioned and positioned such that the transfer shaft axis intersects an adjusting line which is perpendicular to a reference plane that is spanned by the first and second crankpin axes and which adjusting line intersects the crankshaft axis. Depending on the angle between the neighbouring crankpins about the crankshaft axis the transfer shaft axis intersects the adjusting line at a certain location. This location may lie at the crankshaft axis or eccentrically thereof. The first intermediate transfer gears may be rotatably mounted to the second crank web through a separate supporting element that is fixed to the second crank web and / or the second intermediate transfer gears may be rotatably mounted to the third crank web through a separate supporting element that is fixed to the third crank web.

[0050] 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. For example, it is possible that the first and second intermediate transfer gears are rotatably mounted to the second and third crank webs, respectively, in a different manner.

Claims

1. A crankshaft (1, 40) for an internal combustion engine including variable compression ratio comprising a main journal (2a, 42a) including a crankshaft axis (5, 41), a first crankpin (3a, 43a), a first and second crank web (4a, 4b, 44a, 44b) at opposite sides of the first crankpin (3a, 43a), a second crankpin (3b, 43b), a third and fourth crank web (4c, 4d, 44c, 44d) at opposite sides of the second crankpin (3b, 43b), wherein the second and third crank web (4b, 4c, 44b, 44c) are adjacent to each other and the first crank web (4a, 44a) is adjacent to the main journal (2a, 42a), a first eccentric member (6a, 45a) which is rotatably mounted on the first crankpin (3a, 43a) and which comprises a first bearing portion (8a, 46a) for supporting a big end of a connecting rod and an external first eccentric member gear (10, 47) located between the first bearing portion (8a, 46a) and the second crank web (4b, 44b), a second eccentric member (6b, 45b) which is rotatably mounted on the second crankpin (3b, 43b) and which comprises a second bearing portion (8b, 46b) for supporting a big end of a connecting rod and an external second eccentric member gear (23, 48) located between the second bearing portion (8b, 46b) and the third crank web (4c, 44c), a transfer shaft (19, 50) which extends through the second and third crank web (4b, 4c, 44b, 44c) and which is rotatable with respect to the second and third crank web (4b, 4c, 44b, 44c) about a transfer shaft axis, wherein an external first transfer gear (18, 52) is fixed to the transfer shaft (19, 50) at a side of the second crank web (4b, 44b) where the first eccentric member (6a, 45a) is located and an external second transfer gear (21, 49) is fixed to the transfer shaft (19, 50) at a side of the third crank web (21, 44c) where the second eccentric member (6b, 45b) is located, wherein the first and second eccentric members (6a, 6b, 45a, 45b) are drivably coupled to each other through the transfer shaft (19, 50) such that rotation of the first eccentric member (6a, 45a) about the first crankpin (3a, 43a) causes the second eccentric member (6b, 45b) to rotate about the second crankpin (3b, 43b) by the same angle and in the same direction, characterized in that the first and second transfer gears (18, 21, 49, 52) mesh with external first and second intermediate transfer gears (17, 22, 51), respectively, which in turn mesh with the first and second eccentric member gears (10, 23, 47, 48), wherein the first and second intermediate transfer gears (17, 22, 51) are rotatably mounted to the second and third crank webs (4b, 4c, 44b, 44c), respectively.

2. A crankshaft (1, 40) according to claim 1, wherein the main journal is a first main journal (2a, 42a), wherein the second and third crank webs (4b, 4c, 44b, 44c) are interconnected through a second main journal (2b, 42b), wherein the transfer shaft (19, 50) also extends through the second main journal (2b, 42b).

3. A crankshaft (1, 40) according to claim 1 or 2, wherein the transfer shaft axis coincides with the crankshaft axis (5, 41).

4. A crankshaft (1, 40) according to any one of the preceding claims, wherein the first and second transfer gears are identical (18, 21, 49, 52) and / or the first and second intermediate transfer gears (17, 22, 51) are identical and / or the first and second eccentric member gears (10, 23, 47, 48) are identical.

5. A crankshaft (1, 40) according to any one of the preceding claims, wherein the first intermediate transfer gear is one of two first intermediate transfer gears (17) which mesh with both the first eccentric member gear (10, 47) and the first transfer gear (18, 52), wherein both first intermediate transfer gears (17) are rotatably mounted to the second crank web (4b, 44b), and / or wherein the second intermediate transfer gear is one of two second intermediate transfer gears (22, 51) which mesh with both the second eccentric member gear (23, 48) and the second transfer gear (21, 49), wherein both second intermediate transfer gears (22, 51) are rotatably mounted to the third crank web (4c, 44c).

6. A crankshaft (1) according to any one of the preceding claims, wherein the first eccentric member (6a) has an external main eccentric member gear (9) which is located between the first bearing portion (8a) and the first crank web (4a), wherein the main eccentric member gear (9) is drivably coupled to an auxiliary gear (12) through an external main intermediate gear (11), which auxiliary gear (12) is fixed to an auxiliary shaft (14) which in turn extends through the first crank web (4a) and the main journal (2a) and which is rotatable with respect to the main journal (2a) and the first crank web (4a), wherein the main intermediate gear (11) is rotatably mounted to the first crank web (4a) at a side of the first crank web (4a) where the first eccentric member (6a) is located.

7. A crankshaft (1, 40) according to any one of the preceding claims, wherein the first intermediate transfer gear (17) is mounted to a first intermediate transfer gear shaft (13') that is radially supported by both the second crank web (4b) and a separate supporting element (16'), which is attached to the second crank web (4b) at a circumferential side thereof or by a separate supporting element (53), which is attached to the second crank web (44b) at a side where the first eccentric member (46a) is located or at a circumferential side thereof and / or wherein the second intermediate transfer gear (23) is mounted to a second intermediate transfer gear shaft (13'') that is radially supported by both the third crank web (4c) and a separate supporting element (16''), which is attached to the third crank web (4c) at a circumferential side thereof or by a separate supporting element (53), which is attached to the third crank web (44c) at a side where the second eccentric member (46b) is located or at a circumferential side thereof.

8. A crankshaft (1, 40) according to any one of the preceding claims, wherein the first crankpin (3a, 43a) includes a first crankpin axis and the second crankpin (3b, 43b) includes a second crankpin axis, wherein the first intermediate transfer gear is one of two first intermediate transfer gears (17) which mesh with both the first eccentric member gear (10, 47) and the first transfer gear (18, 52), wherein both first intermediate transfer gears (17) are rotatably mounted to the second crank web (4b, 44b), wherein the second intermediate transfer gear is one of two second intermediate transfer gears (22, 51) which mesh with both the second eccentric member gear (23, 48) and the second transfer gear (21, 49), wherein both second intermediate transfer gears (22, 51) are rotatably mounted to the third crank web (4c, 44c), wherein the first and second transfer gears (18, 52, 29, 41) are the same and the first and second eccentric member gears (10, 47, 23, 48) are the same, wherein the first and second intermediate transfer gears (17, 22, 51) are dimensioned and positioned such that the transfer shaft axis intersects an adjusting line which is perpendicular to a reference plane that is spanned by the first and second crankpin axes and which adjusting line intersects the crankshaft axis(5, 41) .

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