Semi-built crankshaft for large turbocharged two-stroke single-flow crosshead internal combustion engine

Abstract

A semi-built-up crankshaft for a large turbocharged two-stroke single-flow crosshead internal combustion engine, having crank throws (3) which are connected together by main journal pins (1), said main journal pins having a main journal pin central part (1b) and two cylindrical main journal pin end parts (1a), said cylindrical main journal pin end parts being inserted into holes in associated crank arms, wherein in order to reduce stress concentration in the transition region between the main journal pin central part and the main journal pin end parts, the crankshaft includes fillets (11), at least some of said fillets being provided only in the respective main journal pins. This enables a crank throw design to have improved fatigue safety of the main journal pin fillets and an undiminished (or even improved) torque capacity without increasing the cylinder distance and the overall length of the engine. Additionally, there is no need to machine the crank arms, thus making the length of the shrink-fit connection independent of the main journal pin fillet radius.

Description

Technical Field

[0001] The present invention relates to a semi-built-up crankshaft for a large turbocharged two-stroke uniflow crosshead internal combustion engine, the semi-built-up crankshaft having crank throws, the crank throws including crank pins with two crank arms, each crank arm having a hole, the crank throws being connected together by main journal pins, the main journal pins having a central part of the main journal pin with a diameter of D c and two cylindrical end parts of the main journal pin with a diameter of D s the cylindrical end parts of the main journal pin being inserted into the holes of the associated crank arms, wherein in order to reduce stress concentration in the transition region between the central part of the main journal pin and the end parts of the main journal pin, the crankshaft includes fillets in the main journal pins, wherein at least some of the fillets in the main journal pins are provided only in the respective main journal pins. Background Art

[0002] Large turbocharged two-stroke uniflow crosshead internal combustion engines are commonly used as prime movers for large ocean-going vessels (e.g., tankers and container ships) or power plants.

[0003] Crankshafts of the above type are well known, for example from US1136524A. Due to their size, the crankshafts for large two-stroke internal combustion engines are semi-built-up, i.e., manufactured from smaller parts and then assembled. In the drawings, Figure 1 an example of a semi-built-up crankshaft 20 is shown, Figure 2 showing the main parts of the semi-built-up crankshaft 20. The semi-built-up crankshaft 20 includes a plurality of cylinder parts, one cylinder part corresponding to each cylinder of the respective engine. Referring to Figure 1 , each crankshaft cylinder part 3, commonly referred to as a crank throw 3, consists of a crank pin 4 and two crank arms 5, the crank arms 5 being mounted on each side of the crank pin. See Figure 2 , each crank arm 5 has a hole 6, and the end parts 1a of the respective main journal pin 1 are inserted into each of the holes 6 in order to connect the plurality of crank throws 3 together.

[0004] When assembling the semi-built-up crankshaft 20, the main journal pins 1 are inserted into the holes 6 of the crank arms 5 and connected to the crank arms 5 of the respective crank throws 3 by a shrink-fit connection, i.e., the journal pins have an oversize dimension relative to the diameter of the holes 6 in the crank arms 5. After assembly, the entire crankshaft is machined on a large lathe to create the final main journals and crank pin journals, thereby ensuring the collinearity of all journals.

[0005] Referring to Figure 1 , 2And 3, during the final machining of the crankshaft 20, in order to reduce the stress concentration in the transition region between the central portion 1b of the main journal pin and the end portion 1a of the main journal pin, it is known practice to form a fillet 11 on the main journal pin 1, where the diameter increases from the central diameter D of the main journal pin c to the reduced diameter D at the end portion 1a of the main journal pin s . These fillets 11 are referred to as main journal pin fillets 11. At the same time, a fillet 12 on the crank arm 5 at the hole 6 around the shrink-fit connection between the crank arm 5 and the end portion 1a of the main journal pin is also machined to ensure a perfect smooth transition from the main journal pin 1 to the crank arm 5. Thus, a fillet 13 composed of the main journal pin fillet 11 and the machined fillet 12 on the crank arm 5 is located at the transition between the main journal pin 1 and the hole 6 in the crank arm 5. The length L of the shrink-fit connection corresponds to the axial extension length of the hole 6 in the crank arm 5 minus the depth of the fillet 12

[0006] Engines with increasing power and decreasing size are limited by the torque that a semi-built-up crank can transmit and the dynamic loads it can withstand. The torque capacity is determined by simple geometric measurements such as the shrink-fit connection length L, the oversize / diameter interference, and the diameters of the shaft and the hub, while the stress is controlled by the diameter D of the central portion 1b of the main journal pin (see Figure 2 ) and the radius of the fillet 11 on the main journal pin 1 c . Increasing the shrink-fit connection length L and the main journal pin fillet radius is the simplest way to increase these two parameters, but in both cases, it will result in an increase in the cylinder spacing and thus an increase in the total weight of the engine. Recognizing that the design goal of a new engine is to improve performance and reduce cost (by weight), the existing relationship between the shrink-fit connection length, the main journal pin fillet radius, and the cylinder spacing is disadvantageous Summary of the Invention

[0007] The object of the present invention is to provide a semi-built-up crankshaft of the type mentioned in the introduction, which has a fillet in the transition region between the central portion of the main journal pin and the end portion of the main journal pin, and at least significantly reduces the above-mentioned challenges related to the transmissible torque and dynamic loads it can withstand

[0008] The foregoing and other objects are achieved by the features of the technical solution claimed in this application. Further embodiments become apparent from the description and the drawings

[0009] According to a first aspect, there is provided a semi-built-up crankshaft for a large turbocharged two-stroke single-flow crosshead internal combustion engine, the crankshaft having a crank throw, the crank throw including a crankpin having two crank arms, each crank arm having a hole, and the crank throws being connected together by a main journal pin, the main journal pin having a diameter of D cThe central part of the main journal pin and two cylindrical end parts of the main journal pin with a diameter of D s The cylindrical end parts of the main journal pin are inserted into the holes of the associated crank arms. In order to reduce the stress concentration in the transition region between the central part of the main journal pin and the end parts of the main journal pin, the crankshaft includes fillets in the main journal pins, where at least some of the fillets in the main journal pins are solely provided in the respective main journal pins, and it is characterized in that the diameter D of the end part of the main journal pin s is larger than the diameter D of the central part of the main journal pin c and the fillets are made in the end faces of the respective end parts of the main journal pin, and the end faces face the central part of the main journal pin.

[0010] Therefore, by solely providing fillets in the main journal pins as proposed, the shrink-fit connection length L and the resulting torque capacity are no longer associated with the radius of the fillets in the main journal pins. This enables the crank design to have improved fatigue safety of the fillets in the main journal pins and an undiminished (even improved) torque capacity without increasing the cylinder spacing and the overall length of the engine. Additionally, machining of the crank arms is not required, thus making the shrink-fit connection length independent of the radius of the fillets in the main journal pins.

[0011] For optimal results, it is preferred that the fillets solely made in the main journal pins are made as circular fillets. Further, it is preferred that these fillets extend all the way around the main journal pin.

[0012] In principle, the geometry of the fillets in the main journal pins can be distinguished, where each fillet is provided as a complete fillet at the top and as a reduced fillet at the bottom of the main journal pin because the load is highest in the half of the fillet closest to the crank pin. Therefore, the geometry of the fillets in the main journal pins can be made asymmetric because the fillets in the main journal pins of the semi-built-up crankshaft according to the present invention can be made before assembling the crankshaft.

[0013] In fact, the fillets can have any suitable form that reduces the stress concentration in the transition region between the central part of the main journal pin and the end parts of the main journal pin. Thus, in a preferred embodiment of the present invention, the fillets have a surface which, when viewed in cross-section, includes a plurality of circular segments, each circular segment having a radius of curvature. Further preferably, the sum of the angles of the plurality of circular segments is at least 120 degrees of a full circle, preferably at least 150 degrees of a full circle, and most preferably at least 180 degrees of a full circle.

[0014] As visible in cross-section, the surface of the fillets can additionally include a plurality of linear segments.

[0015] The actual design of the rounded corner depends on the selected circular section and linear section and defines the height of the rounded corner.

[0016] To ensure that the strength of the end portion of the main journal pin is sufficient to provide an effective shrink-fit connection portion whose length corresponds to the axial extension length of the corresponding hole in the crank arm, the end portion of the main journal pin should preferably be provided with an annular lip around the corresponding rounded corner, and the lip has a suitable height.

[0017] To correlate the length of the shrink-fit connection portion with the radius of the rounded corner of the main journal pin in the proposed manner, the diameter of the end portion of the main journal pin should be increased relative to a known crankshaft and should be greater than the diameter of the central portion of the main journal pin of the main journal pin. Therefore, the diameter of the end portion of the main journal pin should be greater than the diameter of the central portion of the main journal pin, at least as large as twice the height of the annular rounded corner visible in the cross-section plus twice the height of the annular lip. Therefore, the estimation for different engine sizes shows that the ratio D s / D c should be in the range of 1.1 to 2.

[0018] As visible in the cross-section, the height of each rounded corner should preferably be between 1% and 10% of the diameter of the central portion of the main journal pin, and most preferably about 3%. In addition, the height of the annular lip should preferably be between 0.5% and 5% of the diameter of the central portion of the main journal pin, and most preferably about 1.5%.

[0019] Therefore, to provide sufficient space in the end portion of the main journal pin to accommodate a rounded corner and an annular lip with sufficient height, it is preferred that the diameter of the end portion of the main journal pin is at least 10% larger than the diameter of the central portion of the main journal pin of the main journal pin, preferably 25% larger, and most preferably 50% larger. This allows the main journal pin to be made with the rounded corner as described, where a rounded corner with a relatively large radius can be obtained completely inside the main journal pin. Additionally, the end portion of the main journal pin can include an annular lip around the annular rounded corner in this way, so as to provide a shrink-fit connection portion having a length approximately equal to that without making the rounded corner.

[0020] In the most preferred embodiment of the present invention, as visible in the cross-section, the surface of the rounded corner extends at least 180 degrees of a full circle, because the length of the shrink-fit connection portion is thereby as large as possible, thus providing the maximum ability to transmit torque at the selected arm thickness.

[0021] By using high-specification materials with higher fatigue strength and yield strength, higher torque capacity and safety of the rounded corner of the main journal pin can be obtained. However, high-specification materials are much more expensive, and not all crankshaft manufacturers can easily obtain such materials. The proposed design provides similar benefits by using widely available standard materials. Description of the Drawings

[0022] The present invention will be explained in more detail with reference to the exemplary embodiments shown in the accompanying drawings, wherein:

[0023] Figure 1 An example of a known semi-built-up crankshaft is shown.

[0024] Figure 2 Shows Figure 1 The main parts of the semi-built-up crankshaft shown.

[0025] Figure 3 Shows in more detail Figure 1 The parts of the semi-built-up crankshaft shown.

[0026] Figure 4 Shows in more detail the parts of a semi-built-up crankshaft according to an embodiment of the present invention, and

[0027] Figure 5 Shows an example of a fillet design for a semi-built-up crankshaft according to the present invention. Detailed Description

[0028] Figure 1 、 2 Figures 3 show examples of known semi-built-up crankshafts, which are described in detail in the introductory part of the foregoing specification.

[0029] In Figure 4 a cross-section of an embodiment of a semi-built-up crankshaft according to the present invention can be seen. In Figure 4 the same reference numerals as in Figure 1 、 2 and 3 are used for corresponding elements.

[0030] In Figure 4 on the left side of, a crank arm 5 having a hole 6 and a part of a main journal pin 1 having a central portion 1b and an end portion 1a of the main journal pin can be seen. As shown, the end portion 1a of the main journal pin 1 is inserted into the hole 6 of the crank arm 5, wherein it is typically connected to the crank arm 5 using a shrink fit connection, i.e., the main journal pin 1 has an oversized dimension relative to the diameter of the hole 6 in the crank arm 5. The length L of the shrink fit connection substantially corresponds to the axial extension length of the hole 6 in the crank arm 5.

[0031] To reduce stress concentration in the transition region between the central portion 1b of the main journal pin and the end portion 1a of the main journal pin, where the diameter increases from the central diameter D c of the main journal pin to the shrink diameter D s of the end portion 1a of the main journal pin, it is common practice to create a fillet 11 on the main journal pin 1.

[0032] According to the present invention, the fillet 11 is provided only in the respective main journal pins 1, and preferably by machining in the end face 1c of the respective main journal pin end portion 1a of the main journal pin 1, the end face 1c facing the main journal pin central portion 1b. Thus, the length L of the shrink fit connection is as long as the selected dimensions of the crank arm 5 and the hole 6 therein, and the resulting torque capacity of the crankshaft 20 is no longer associated with the radius of the fillet of the main journal pin, because there is no machined fillet or a part of the crank arm 5 or a part of the main journal pin end portion 1a in the region where these elements intersect, except for the small chamfer 2, which may be formed on the edge of the main journal pin end portion facing the main journal pin central portion to ensure a high shrinkage pressure at the end of the shrink fit connection. Since the high shrinkage pressure limits the micro-slip and fretting wear in the shrink fit connection, the high shrinkage pressure is advantageous. The torque capacity can be maintained or even increased without increasing the cylinder spacing and the overall length of the engine.

[0033] As can be seen, the fillet 11 is made as an annular fillet 11 extending around the main journal pin 1 in a full circle.

[0034] In an exemplary embodiment of the present invention, as Figure 5 can be seen, the fillet 11 has a surface 30, which in cross-section includes: three circular segments 30a, 30b and 30c, each circular segment having a radius of curvature of R 1 、R 2 and R 3 ; and two linear segments 30d and 30e, where the linear segment 30e is located at the bottom of the fillet 11. The sum of the angles of the circular segments is greater than 180 degrees in the shown embodiment, in fact about 194 degrees.

[0035] In Figure 5 the shown embodiment, the fillet 11 is provided with an undercut 30u in the circular segment 30a, and this segment thus extends a short distance into the central portion 1b of the main journal pin 1. This undercut 30u is used to ensure that the edge of the bearing shell (not shown) connected to the main journal pin 1 does not impact the fillet 11 when the crankshaft is subjected to abnormal axial vibration, but most importantly it enables the pre-assembly machinability of the main journal pin fillet 11. The collinearity of the bearing surfaces is ensured by the post-assembly machining of the bearing surfaces, which would not be possible without the undercut.

[0036] The actual design of the fillet 11 depends on the selected circular and linear segments and defines the height H f . Figure 5 The shown embodiment is only an illustrative example and an infinite number of other feasible embodiments can be envisaged, where the actual design depends on many other design criteria, such as engine size, dynamic loads, etc.

[0037] As Figure 4 and Figure 5 shown, the end portion 1a of the main journal is provided with an annular lip 8 surrounding the respective fillet 11. The lip 8 is provided with a suitable height H l to ensure that the lip 8 has sufficient stiffness to ensure that the length L of the high-pressure shrink-fit connection corresponds to the axial extension length of the respective hole 6 in the crank arm 5.

[0038] In order to relate the shrink-fit connection length L to the radius of the main journal pin fillet 11 in the proposed manner, the diameter D of the end portion of the main journal pin 1 s should be increased relative to a known crankshaft and should be greater than the diameter D of the central portion 1b of the main journal pin 1 of the main journal pin c . Thus, the diameter D of the end portion 1a of the main journal pin 1 s should be greater than the diameter D of the central portion 1b of the main journal pin 1 of the main journal pin c and as large as at least twice the height H of the annular fillet 11 visible in cross-section plus twice the height H f of the annular lip 8. Thus, estimates for different engine sizes indicate that the ratio D l / D s should be in the range of 1.1 to 2. c

[0039] As visible in cross-section, the height H of each fillet 11 f should preferably be between 1% and 10% of the diameter of the central portion 1b of the main journal pin 1 of the main journal pin, more preferably between 2% and 5%, and most preferably about 3%. In addition, the height H of the annular lip 8 l should preferably be between 0.5% and 5% of the diameter of the central portion 1b of the main journal pin 1 of the main journal pin, and most preferably about 1.5%.

[0040] Therefore, in order to provide sufficient space in the end portion 1a of the main journal pin to accommodate both the fillet 11 and the annular lip 8 having sufficient height, it is preferred that the diameter D of the end portion 1a of the main journal pin 1 s is at least 10% larger than the diameter D of the central portion 1b of the main journal pin 1 of the main journal pin c , preferably 25% larger, and most preferably 50% larger. This allows the main journal pin 1 to be made with the fillet 11 as described, where it is possible to obtain a fillet 11 with a relatively large radius intact inside the main journal pin 1. Additionally, in this way, the end portion 1a of the main journal pin 1 can include an annular lip 8 that surrounds the annular fillet 11, thus providing a shrink-fit connection with a length L that is approximately equal to that without the fillet 11 being manufactured.

[0041] ​In the most preferred embodiment of the present invention, as seen in cross-section, the surface of the rounded corner 11 extends through at least 180 degrees of a full circle because the length L of the shrink-fit connection is as large as possible, thus providing the maximum ability to transmit torque at the selected arm thickness.

Claims

1. A semi-built-up crankshaft (20) for a large turbocharged two-stroke single-flow crosshead internal combustion engine, said semi-built-up crankshaft having crank throws (3), said crank throws including crank pins (4) with two crank arms (5), each of said crank arms (5) having a hole (6), said crank throws (3) being connected together by main journal pins (1), said main journal pins having a main journal pin central part (1b) and two cylindrical main journal pin end parts (1a), said main journal pin central part having a diameter D c , said cylindrical main journal pin end parts having a diameter D s , said cylindrical main journal pin end parts being inserted into the holes (6) of the associated crank arms (5), wherein in order to reduce stress concentration in the transition region between said main journal pin central part (1b) and said main journal pin end parts (1a), said crankshaft (20) includes fillets (11), wherein at least some of said fillets (11) in said main journal pins (1) are provided only in the respective main journal pins (1), It is characterized in that The diameter D of the end portion (1a) of the main journal pin s is greater than the diameter D of the central portion (1b) of the main journal pin c , and at least some of the rounded corners are formed in the end face (1c) of the corresponding end portion (1a) of the main journal pin (1), the end face (1c) facing the central portion (1b) of the main journal pin; and the end portion (1a) of the main journal pin is provided with an annular lip (8) around the corresponding rounded corner (11), the annular lip (8) having an appropriate height, the height H of the annular lip (8) l is between 0.5% and 5% of the diameter D of the central portion (1b) of the main journal pin (1) c .

2. The semi-built-up crankshaft according to claim 1, It is characterized in that At least some of the fillets are made into circular fillets.

3. The semi-built-up crankshaft according to claim 1 or 2, It is characterized in that At least some of the fillets extend around the main journal pin (1) for a full circle.

4. The semi-built-up crankshaft according to claim 1 or 2, It is characterized in that At least some of the rounded corners have a surface (30) which, when viewed in cross-section, comprises a plurality of circular segments (30a, 30b, 30c), each circular segment having a radius of curvature (R 1 , R 2 , R 3 ), wherein the sum of the angles of the plurality of circular segments (30a, 30b, 30c) is at least 120 degrees of a full circle.

5. The semi-built-up crankshaft according to claim 4, It is characterized in that The sum of the angles of the plurality of circular segments (30a, 30b, 30c) is at least 150 degrees of a full circle.

6. The semi-built-up crankshaft according to claim 5, It is characterized in that The sum of the angles of the plurality of circular segments (30a, 30b, 30c) is at least 180 degrees of a full circle.

7. The semi-built-up crankshaft according to claim 4, It is characterized in that When viewed in cross-section, the surface of at least some of the fillets includes a plurality of linear segments (30d, 30e).

8. The semi-built-up crankshaft according to claim 1 or 2, It is characterized in that Ratio D s / D c is in the range of 1.1 to 2.

9. The semi-built-up crankshaft according to claim 1 or 2, It is characterized in that In cross-section, the height H of each of said at least some fillets f is between 1% and 10% of the diameter D of the central part (1b) of said main journal pin (1). c ​ 10. The semi-built-up crankshaft according to claim 9, It is characterized in that In cross-section, the height H of each of said at least some rounded corners f is between 2% and 5% of the diameter D of the central part (1b) of said main journal pin (1) of said main journal pin c pin.

11. The semi-built-up crankshaft according to claim 10, It is characterized in that In a cross-sectional view, the height H of each of the at least some of the rounded corners f is 3% of the diameter D of the central part (1b) of the main journal pin (1) of the main journal pin c .

12. The semi-built-up crankshaft according to claim 1 or 2, It is characterized in that The height H of the annular lip (8) l is 1.5% of the diameter D of the central part (1b) of the main journal pin (1) of the main journal pin c .

13. The semi-built-up crankshaft according to claim 1 or 2, It is characterized in that The diameter D of the main journal pin end portion (1a) of the main journal pin (1) s is at least 10% larger than the diameter D of the main journal pin central portion (1b) of the main journal pin (1). c by 10%.

14. The semi-built-up crankshaft according to claim 13, It is characterized in that The diameter D of the end portion (1a) of the main journal pin (1) of the main journal pin s is 25% larger than the diameter D of the central portion (1b) of the main journal pin (1) of the main journal pin c by 25%.

15. The semi-built-up crankshaft according to claim 13, It is characterized in that The diameter D of the end portion (1a) of the main journal pin (1) of the main journal pin s is 50% larger than the diameter D of the central portion (1b) of the main journal pin (1) of the main journal pin c by 50%.

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