DK181184B1

DK181184B1 - A semi-built crankshaft for large turbocharged two-stroke uniflow crosshead internal combustion engine

Info

Publication number: DK181184B1
Application number: DKPA202200143A
Authority: DK
Inventors: Illum Munthe Mark
Original assignee: Man Energy Solutions Filial Af Man Energy Solutions Se Tyskland
Priority date: 2022-02-22
Filing date: 2022-02-22
Publication date: 2023-04-12
Also published as: CN116641955A; JP7425234B2; JP2023122543A; DK202200143A1; KR102642310B1; KR20230126185A

Abstract

Described is a semi-built crankshaft (20) for a large turbocharged two-stroke uniflow crosshead internal combustion engine having crank throws (3) comprising a crank pin (4) with two crank webs (5), each of which crank webs (5) has a hole (6), which crank throws (3) are joined together by means of main journal pins (1) with a central main journal pin section (1b) and two cylindrical main journal pin end sections (1a) which are inserted in the hole (6) of the associated crank web (5), where said crankshaft (20) comprises fillets (11) in order to reduce stress concentrations in the transition zones between the central main journal pin section (1b) and the main journal pin end sections (1a). The crank shaft (20) is peculiar in that at least some of said fillets (11) in the main journal pins are provided solely in the respective main journal pin (1). Hence, by providing the fillets (11) in the main journal pins (1) as suggested, the shrink fit connection length L and the resulting torque capacity is no longer coupled to the main journal pin fillet radius. This enables a crank throw (3) design with increased main journal pin fillet safety against fatigue and uncompromised (or even improved) torque capacity without increasing the cylinder distance and overall engine length. In addition, no machining of the crank web (5) is required, thereby making the shrink fit connection length independent from main journal pin fillet radius.

Description

DK 181184 B1 1

TECHNICAL FIELD

The present invention relates to a semi-built crankshaft for a large turbocharged two-stroke uniflow crosshead internal combustion engine having crank throws comprising a crank pin with two crank webs, each of which crank webs has a hole, which crank throws are joined together by means of main journal pins with a central main journal pin section having a diameter Dc and two cylindrical main journal pin end sections having a diameter Ds and which are inserted in the hole of the associated crank web, where said crankshaft comprises fillets in the main journal pins in order to reduce stress concentrations in the transition zones between the central main journal pin section and the main journal pin end sections, where at least some of said fillets in the main journal pins are provided solely in the respective main journal pin.

BACKGROUND OF THE INVENTION

Large turbocharged two-stroke uniflow crosshead internal combustion engines are typically used as prime movers in large ocean going ships, such as tanker and container ships or in power plants.

Crankshafts of the above mentioned kind are well known, e.g. from US 1.136.524 A. Due to their size crankshafts for large two-stroke internal combustion engines are semi-built, i.e. manufactured in smaller parts which are subsequently assembled. In the attached drawings, Fig. 1 shows an example of a semi-built crankshaft 20 and Fig. 2 shows essential parts of the semi-built crankshaft 20. The semi-built crankshaft 20 comprises a number of cylinder sections, one for each cylinder of the respective engine. With reference made to Fig. 1, each crankshaft cylinder section 3, often referred to as a crank throw 3, consists of two crank webs 5 and a crank pin 4 one at each side of which the crank webs 5 are mounted. Each crank web 5, see Fig. 2, has a hole 6, into

DK 181184 B1 2 each of which hole 6 an end section 1a of a respective main journal pin 1 is inserted in order to join a number of crank throws 3 together.

When assembling a semi-built crankshaft 20, the main journal pins 1 are inserted into a hole 6 in a crank web 5 and joined with the crank web 5 of the respective crank throws 3 using a shrink fit connection, i.e. the journal pin has an oversize in relation to the diameter of the hole 6 in the crank web 5. Once assembled, the entire crankshaft is machined in a large lathe to create the finalized main- and crank pin journals to ensure collinearity of all journals.

With reference to Fig. 1, 2 and 3, during final machining of the crankshaft 20, known practice is to create fillets 11 on the main journal pins 1 in order to reduce stress concentrations in the transition zones between the central main journal pin section 1b and the main journal pin end sections 1a, where the diameter increase from a central main journal pin diameter Dc to a shrink diameter Ds at the main journal pin end sections 1a. These fillets 11 are referred to as the main journal pin fillets 11. At the same time, a fillet 12 on the crank web 5 at the hole 6 around the shrink fit connection between the crank web 5 and the main journal pin end sections 1a is also machined to ensure a perfectly smooth transition from the main journal pin 1 to the crank web 5. Hence, a fillet 13 consisting of a main journal pin fillet 11 and a machined fillet 12 on the crank web 5 is positioned at the transition between the main journal pin 1 and the hole 6 in the crank web 5. The shrink fit connection has a length L corresponding to the axial extension of the hole 6 in the crank web 5 minus the — depth of the fillet 12.

Increasingly powerful and compact engines are limited by the torque that the semi-built crank throw can transmit and the dynamic loads it can sustain. The torque capacity is determined by simple geometric measures such as the shrink fit connection length L, oversize/diametric interference and the diameters of the shaft and the hub, while stresses are governed by the diameter De of the central section of the main journal pin 1b (see Fig. 2) and the radius of the fillet 11 on the main journal pin 1. Increasing the shrink fit connection length L and the

DK 181184 B1 3 main journal pin fillet radius are the simplest ways to increase both these parameters, but in both cases doing so, leads to increased cylinder distance and hence increased overall engine weight. Recognizing that the design objectives for new engines are to increase performance and to decrease cost (by weight), the existing coupling between shrink fit connection length, main journal pin fillet radius and cylinder distance is unfavorable.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a semi-built crankshaft of the kind mentioned in the introduction having fillets in the transition zones between the central main journal pin section and the main journal pin end sections, where the above mentioned challenges relating to transmittable torque and dynamic loads it can sustain are at least significantly reduced.

The foregoing and other objects are achieved by the features of the independent claims. Further implementation forms are apparent from the dependent claims, the description, and the figures.

According to a first aspect, there is provided a semi-built crankshaft for a large turbocharged two-stroke uniflow crosshead internal combustion engine having crank throws comprising a crank pin with two crank webs, each of which crank webs has a hole, which crank throws are joined together by means of main journal pins with a central main journal pin section having a diameter Dc and two cylindrical main journal pin end sections having a diameter Ds and which are inserted in the hole of the associated crank web, where said crankshaft comprises fillets in the main journal pins in order to reduce stress concentrations in the transition zones between the central main journal pin section and the main journal pin end sections, where at least some of said fillets in the main journal pins are provided solely in the respective main journal pin and being characterized in that the diameter Ds of the main journal pin end sections is larger than the diameter De of the central main journal pin section, and said fillets are made in an end surface of the respective main journal pin

DK 181184 B1 4 end section of the main journal pin, which end surface facing the central main journal pin section.

Hence, by providing the fillets solely in the main journal pins as suggested, the shrink fit connection length L and the resulting torque capacity is no longer coupled to the radius of the main journal pin fillet. This enables a crank throw design with increased main journal pin fillet safety against fatigue and uncompromised (or even improved) torque capacity without increasing the cylinder distance and overall engine length. In addition, no machining of the crank web is required, thereby making the shrink fit connection length independent from main journal pin fillet radius.

In order to obtain the optimum effect it is preferred that the fillets made solely in said main journal pins are made as annular fillets. Further, it is preferred that — these fillets are extending all the way around the main journal pin.

In principle, the geometry of the fillets in the main journal pins could be differentiated, where each fillet is provided as a full fillet at the top and as a reduced fillet at the bottom of the main journal pin as the load is highest in the half of the fillet closest to the crank pin. Thus, the geometry of the fillets in the main journal pins could be made asymmetric, because the fillets in the main journal pins of the semi-built crank shaft according to the invention may be made before the crank shaft is assembled.

The fillets may in practice have any suitable form that reduce the stress concentrations in the transition zones between the central main journal pin section and the main journal pin end sections. Thus, in a preferred embodiment of the invention said fillets have a surface, which seen in cross section comprises a number of circle sections each having a radius of curvature. It is further preferred that the angular sum of said number of circle sections is at least 120 angular degrees, preferably at least 150 angular degrees and most preferably at least 180 angular degrees of a full circle.

DK 181184 B1

The surface of said fillets, as seen in cross section, may in addition comprise a number of linear sections.

The actual design of the fillets depends on the selected circle and linear 5 sections and defines a height of the fillets.

In order to ensure that the strength of the main journal pin end sections is sufficient to provide an effective shrink fit connection with a length corresponding to the axial extension of the respective hole in the crank web, the main journal pin end sections should preferably be provided with an annular lip surrounding the respective fillet, said lip having an appropriate height.

In order to uncouple the shrink fit connection length from the radius of the main journal pin fillet in the way as suggested, the diameter of end sections of the main journal pin should be increased relative to known crank shafts and be larger than the diameter of the central main journal pin section of the main journal pin. Thus, the diameter of end sections of the main journal pin should be larger than the diameter of the central section of the main journal pin with at least two times the height the annular fillet as seen in cross section plus two times the height of the annular lip. Thus, estimations for different engine sizes indicates that the ratio Ds/Dc should be in the range from 1,1 to 2.

The height of each fillet, as seen in cross section, should preferably be between 1 and 10 %, most preferably about 3 % of the diameter of the central section of the main journal pin. Further, the height of the annular lip should preferably be between 0,5 and 5 %, most preferably about 1,5 % of the diameter of the central main section of the main journal pin.

Thus in order to provide sufficient space in the main journal pin end sections to accommodate a fillet and an annular lip both with sufficient heights, it preferred that the diameter of the end sections of the main journal pin is at least 10 %, preferably 25 % and most preferably 50 % larger than the diameter of the central main journal pin section of the main journal pin. This allows the main

DK 181184 B1 6 journal pin to be made with the described fillets, where fillets with a relatively large radius is allowed to be obtained completely inside the main journal pin. In addition, the end sections of the main journal pin may in this way comprise an annular lip, which surrounds the annular fillet, thus providing a shrink fit connection of approximately the same length as if no fillet was made.

In the most preferred embodiment of the invention the surface of the fillet, seen in cross section, extends over at least 180 angular degrees of a full circle, as the shrink fit connection length hereby is as large as it can be, thus providing the maximum capability to transmit torque with the selected web thickness.

By using high specification materials with higher fatigue and yield strength it is possible to obtain higher torque capacity and main journal pin fillet safety.

However, high specification materials are significantly more expensive and not readily available to all crankshaft manufactures. The proposed design provides similar benefits using standard materials widely available.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained in more details with reference to the example embodiment shown in the drawings, in which:

Fig. 1 shows an example of a known semi-built crankshaft,

Fig. 2 shows essential parts of the semi-built crankshaft shown in Fig. 1,

Fig. 3 shows in greater details parts of the semi-built crankshaft shown in Fig. 1,

Fig. 4. shows in greater details parts of a semi-built crankshaft of an embodiment of according to the invention, and

DK 181184 B1 7

Fig. 5 shows an example of a fillet design for a semi-built crankshaft according to the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Fig. 1, 2 and 3 shows an example of a known semi-built crankshaft, which is described in details above in the introductory part of the description.

In Fig. 4 is seen a section of an embodiment of a semi-built crankshaft according to the invention. In Fig. 4 the same reference numbers are used for corresponding elements as in Fig. 1, 2 and 3.

In left side of Fig. 4 is seen a crank web 5 with a hole 6 and part of a main journal pin 1 having a central main journal pin section 1b and an end section 1a. As shown, the end section 1a of the main journal pin 1 is inserted into the hole 6 of the crank web 5, where it is typically joined with the crank web 5 using a shrink fit connection, i.e. the main journal pin 1 has an oversize in relation to the diameter of the hole 6 in the crank web 5. The shrink fit connection has a length L corresponding approximately to the axial extension of the hole 6 in the crank web 5.

In order to reduce stress concentrations in the transition zone between the central main journal pin section 1b and the main journal pin end sections 1a, where the diameter increase from a central main journal pin diameter Dc to a shrink diameter Ds at the main journal pin end section 1a, it is common practice to create afillet 11 on the main journal pin 1.

According to the invention the fillet 11 is provided solely in the respective main journal pin 1 and, preferably by machining, in an end surface 1c of a respective main journal pin end section 1a of the main journal pin 1, which end surface 1c facing the central main journal pin section 1b. Hereby, the shrink fit connection length L is as long as it can be with the selected dimensions of the crank web 5 and the hole 6 in it, and the resulting torque capacity of the crank shaft 20 is no longer coupled to the radius of the main journal pin fillet, as no fillet or portion

DK 181184 B1 8 of either the crank web 5 or the main journal pin end section 1a is machined in the region where these elements meet, except from a small chamfer 2, which may be created on the edges of the main journal pin end sections facing the central main journal pin section in order to ensure a high shrink pressure at the end of the shrink fit connection. A high shrink pressure is favorable as it limits micro slip and fretting in the shrink fit connection. The torque capacity may be kept or even increased without increasing the cylinder distance and the overall engine length.

As seen, thefillet 11 is made as an annular fillet 11 extending all the way around the main journal pin 1.

In an example embodiment of the invention, as seen in Fig. 5, the fillet 11 has a surface 30, which seen in cross section comprises three circle sections 30a, band c each having a radius of curvature R1, R2 and Rs, and two linear sections 30d and 30e, where said linear section 30e is located in the bottom of the fillet 11. The angular sum of the circle sections is in the shown embodiment more than 180 angular degrees, in fact about 194 angular degrees.

Inthe embodiment shown in Fig. 5 the fillet 11 is provided with an undercut 30u in the circle section 30a, which section hereby extends a small distance into the central main section 1b of the main journal pin 1. This undercut 30u is used to ensure that an edge of a bearing shell (not shown) arranged in connection with the main journal pin 1 does not hit the fillet 11 when the crankshaft is subjected to abnormal axial vibration, but most importantly it enables pre assembly machinability of the main journal pin fillet 11. Collinearity of the bearing surfaces is ensured by post assembly machining of the bearing surfaces, which is not possible without the undercut.

The actual design of the fillet 11 depends on the selected circle and linear sections and defines a height Hr of the fillet 11. The shown embodiment in Fig. 5 is only an illustrative example and an unlimited number of other possible

DK 181184 B1 9 embodiments are conceivable, where the actual design depends on a number of other design criteria, such as engine size, dynamic loads etc.

The main journal end section 1a, as shown in both Fig. 4 and 5, is provided with an annular lip 8 surrounding the respective fillet 11. The lip 8 is provided with an appropriate height Hi to ensure sufficient stiffness of the lip 8 assuring high pressure shrink fit connection with a length L corresponding to the axial extension of the respective hole 6 in the crank web 5.

In order to uncouple the shrink fit connection length L from the radius of the main journal pin fillet 11 in the way as suggested, the diameter Ds of end sections of the main journal pin 1 should be increased relative to known crank shafts and be larger than the diameter De of the central main journal pin section 1b of the main journal pin 1. Thus, the diameter Ds of the end sections 1a of the main journal pin 1 should be larger than the diameter De of the central main journal pin section 1b of the main journal pin 1 with at least two times the height

Hr of the annular fillet 11 as seen in cross section plus two times the height Hi of the annular lip 8. Thus, estimations for different engine sizes indicates that the ratio Ds/Dc should be in the range from 1,1 to 2.

The height Hr of each fillet 11, as seen in cross section, should preferably be between 1 and 10 %, more preferably between 2 and 5 % and most preferably about 3 % of the diameter of the central main section 1b of the main journal pin 1. Further, the height Hi of the annular lip 8 should preferably be between 0,5 and 5 %, most preferably about 1,5 % of the diameter of the central main section 1b of the main journal pin 1.

Thus in order to provide sufficient space in the main journal pin end sections 1a to accommodate a fillet 11 and an annular lip 8 both with sufficient heights, itis preferred that the diameter Ds of the end sections 1a of the main journal pin 1 is at least 10 %, preferably 25 % and most preferably 50 % larger than the diameter De of the central main journal pin section 1b of the main journal pin 1. This allows the main journal pin 1 to be made with the described fillets

DK 181184 B1 10 11, where fillets 11 with a relatively large radius is allowed to be obtained completely inside the main journal pin 1. In addition, the end sections 1a of the main journal pin 1 may in this way comprise an annular lip 8, which surrounds the annular fillet 11, thus providing a shrink fit connection of approximately the same length L as if no fillet 11 was made.

In the most preferred embodiment of the invention the surface of the fillet 11, seen in cross section, extends over at least 180 angular degrees of a full circle, as the shrink fit connection length L hereby is as large as it can be, thus providing the maximum capability to transmit torque with the selected web thickness.

Claims

DK 181184 B1 11 Patent claim

1. Semi-built crankshaft (20) for a large turbocharged two-stroke longitudinally scavenged cross-head combustion engine with crank stroke (3) comprising a — crank pin (4) with two crank arms (5), each of the crank arms (5) having a hole (6) which crankshaft layers (3) are connected to each other by means of main bearing pillars (1) with a central main bearing pillar section (1b) with a diameter Dc and two cylindrical main bearing pillar end sections (1a) with a diameter Ds and which are inserted into the hole (6) of the associated crank arm (5), wherein said crankshaft (20) comprises corrugations (11) to reduce stress concentrations in the transition zones between the central main bearing column section (1b) and the main bearing column end sections (1a), wherein at least some of said corrugations (11) in the main bearing columns (1 ) is exclusively provided in the respective main bearing pillar (1), characterized in that the diameter Ds of the main bearing pillar end sections (1a) is greater than the diameter Dc of the central main bearing pillar section (1b), and said roundings (11) are formed in an end face (1c) of the respective main bearing pillar end section (1a) of the main bearing pillar (1), which end face (1c) faces the central main bearing pillar section (1b).

2. Semi-built crankshaft according to claim 1, characterized in that the curves (11) are designed as annular curves (11).

3. Semi-built crankshaft according to claim 1 or 2, characterized in that > the curves (11) extend all the way around the main bearing spindle (1).

4. Semi-built crankshaft according to claims 1-3, characterized in that the curves (11) have a surface (30) which, seen in cross-section, comprises a number of circular sections (30a, b and c), each of which has a radius of curvature (R1, R2 and R3), where the angular sum of said number of circle sections (30a, b and c) is at least 120 angular degrees, preferably at least 150 angular degrees and most preferably at least 180 angular degrees of a full circle.

DK 181184 B1 12

5. Semi-built crankshaft according to claim 4, characterized in that the surface of the curves (11), seen in cross-section, comprises a number of linear sections (30d, 30e).

6. Semi-built crankshaft according to claims 1-5, characterized in that — the main bearing pillar end sections (1a) are provided with an annular lip (8) surrounding the respective rounding (11), which lip (8) has a suitable height.

7. Semi-built crankshaft according to claims 1-6, characterized in that the ratio Ds/Dc is in the range from 1.1 to 2.

8. Semi-built crankshaft according to any one of the preceding claims, characterized in that the height Hr of each rounding (11), seen in cross-section, is between 1 and 10%, more preferably between 2 and 5% and most preferably approx. 3% of the diameter Dc of the central main bearing pillar section (1b) of the main bearing pillar (1).

9. Semi-built crankshaft according to any one of the preceding claims, characterized in that the height Hi of the annular lip (8) is between 0.5 and 5%, most preferably approx. 1.5% of the diameter Dc of the central main bearing pillar section (1b) of the main bearing pillar (1).

10. Semi-built crankshaft according to any one of the preceding claims, characterized in that the diameter Ds of the end sections (1a) of the main bearing pillar (1) is at least 10%, preferably 25% and most preferably 50% greater than the diameter Dc of the central main bearing pillar section (1b) of the main bearing pillar (1).