Preloaded bolt assembly

Abstract

A preload bolt assembly for connecting at least two engine components of a large turbocharged two-stroke uniflow crosshead internal combustion engine is disclosed. [Solution] A preload bolt assembly for connecting at least two engine components (22, 23) of a large turbocharged two-stroke uniflow crosshead internal combustion engine comprises a tie rod (40) and a nut (42), the two engine components being connected by the tie rod and nut, with one end of the tie rod passing through a mounting hole (41) of the engine component and the nut screwed into the threads of the end. This preload bolt assembly is characterized by comprising a braking means disposed on the outer circumference of the tie rod to prevent the tie rod from moving through the mounting hole in the event of failure of the tie rod.

Description

Technical Field

[0001] The present invention relates to a preloading bolt assembly for joining at least two engine components of a large turbocharged two-stroke uniflow crosshead internal combustion engine. However, the engine includes at least one cylinder in a cylinder liner, a reciprocating piston in the cylinder liner, a cylinder cover covering the cylinder, a combustion chamber formed between the reciprocating piston and the cylinder cover in the cylinder liner, a cylinder block, a machine frame, and a bed frame. The at least two engine components are joined by a plurality of tie rods having threads at their ends, and each of the plurality of tie rods has at least one end passed through an attachment hole of at least one of the at least two engine components. A nut for fixing one of the at least two engine components to the other of the at least two engine components is screwed onto the thread at one end of the attachment hole. Background of the Invention

[0002] Large turbocharged two-stroke uniflow crosshead internal combustion engines are typically used as prime movers for large ocean-going vessels such as container ships and power plants. This type of engine is very often operated with heavy oil or fuel oil such as diesel.

[0003] In the large two-stroke engines of the types described above, various engine components are secured together by tie rods. During combustion in the cylinder, a downward force acts on the piston. However, an equivalent upward force acts on the cylinder cover, which is transmitted to the cylinder block, engine frame, and bed plate. In the conventional large two-stroke engines of the types described above, the cylinder cover is secured to the cylinder block by a set of six to eight tie rods. One end of each tie rod is threaded and screwed into a corresponding threaded hole in the cylinder block. The other end passes through a hole in the cylinder cover and is secured by a nut screwed into the threads of the tie rod. This secures the cylinder liner in place. Another set of tie rods extends from the underside of the bed plate to the topside of the cylinder block, securing the engine block, engine frame, and bed plate together. The latter tie rods may pass through tubes welded to the frame. Reinforcements may also be provided at certain positions in these tubes to prevent fatigue failure due to lateral vibration.

[0004] In particular, to absorb the large forces acting on the cylinder cover, cylinder block, and bed plate during the combustion period of the cylinder, all tie rods are pre-loaded with a tensile force of typically more than 1 ton during engine assembly. Therefore, tie rods have internal forces as tensile stress. Consequently, if a tie rod breaks for any reason, it could fly upward and into the engine compartment, potentially causing serious damage to personnel inside the engine compartment or to the engine itself.

[0005] Causes of fracture include not only normal excessive load from the engine itself, but also poor maintenance due to rust, impact marks, material defects, ship vibrations, and manufacturing defects (especially poorly manufactured screw threads).

[0006] The present invention also relates to a large turbocharged two-stroke uniflow crosshead internal combustion engine comprising a preload bolt assembly as described above and in the appended claims. [Overview of the project]

[0007] The object of the present invention is to provide a preload bolt assembly of the type described above, which at least significantly reduces the aforementioned problems relating to tie rod breakage, for connecting at least two engine components of a large turbocharged two-stroke uniflow crosshead internal combustion engine.

[0008] The aforementioned and other issues are resolved by the features described in the independent claims. More specific implementations will become apparent from the dependent claims, specification, and drawings.

[0009] According to the first aspect, a preload bolt assembly for connecting at least two engine components of a large turbocharged two-stroke uniflow crosshead internal combustion engine, The preload bolt assembly comprises at least one tie rod having threads at its end and at least one nut for securing one of the at least two engine components to the other of the at least two engine components. The at least two engine components are connected by the at least one tie rod and the at least one nut, and each of the at least one tie rod has at least one end passing through a mounting hole in at least one of the at least two engine components. The at least one nut is screwed into the threads of the at least one tie rod at one end of the mounting hole. The preload bolt assembly is characterized by comprising a braking means disposed on the outer circumference of at least one of the at least one tie rods, thereby preventing the tie rod from moving through the mounting hole in the event of failure of the tie rod equipped with the braking means.

[0010] Therefore, even if the tie rod breaks, it is prevented from flying upward through the mounting hole of the engine component and into the engine room.

[0011] In principle, the braking means can be formed in any suitable manner to prevent the tie rod from passing through the mounting hole in the event of damage to the tie rod. However, in the first embodiment of the present invention, it is preferable that each of the braking means is positioned on the opposite side of the mounting hole from the nut and has a radial dimension larger than the mounting hole in at least a portion thereof.

[0012] Furthermore, the braking means is preferably provided in the form of a bushing.

[0013] The bushing is preferably rotationally symmetrical in order to provide sufficient grip to the tie rod to which the bushing is provided.

[0014] Furthermore, the bushing is formed to have a conical outer surface at least at the end facing the mounting hole. The diameter of the conical outer surface is smallest at the end facing the mounting hole. The smallest diameter of the conical outer surface is smaller than the diameter of the mounting hole. This allows the bushing to move at least a certain distance within the mounting hole of the engine component in the event of a break in the corresponding tie rod.

[0015] Preferably, at least a portion of the bushing has a conical outer surface end with multiple longitudinally extending slits. In this case, the end with the conical outer surface is divided into multiple segments. If the tie rod through the bushing breaks and the bushing is pushed into the mounting hole of the engine component, the multiple segments can be crushed radially toward the tie rod. This method gradually increases the frictional force between the bushing and the corresponding tie rod, effectively braking the tie rod.

[0016] To allow the bushing to be easily mounted on the tie rod without disassembling the engine, the bushing is preferably composed of at least two divided parts in the longitudinal direction. Alternatively, the bushing may be a single molded piece that is slid onto the tie rod before assembling the tie rod and the cylinder cover.

[0017] The inner diameter of the bushing may be such that, after being mounted to surround the tie rod, its position is maintained by friction between the bushing and the corresponding tie rod. However, it is preferable that the bushing is held in place by a hose clamp attached to the tie rod immediately below the bushing. The bushing may be coated with a friction coating to increase friction between the bushing and the tie rod. Furthermore, the bushing may be provided with integrated screw holes to facilitate assembly, eliminating the need for clamps or similar components.

[0018] The bushing is preferably manufactured from a suitable steel material.

[0019] In a second embodiment of the present invention, it is preferable that each brake means is arranged within the mounting hole.

[0020] Furthermore, the braking means is preferably provided in the form of a sleeve. The sleeve is preferably having a length that at least matches the length of the mounting hole. The sleeve may be loosely mounted in the mounting hole while maintaining a certain clearance between the mounting hole and the sleeve. Alternatively, the sleeve may have an inner diameter that matches the outer diameter of the tie rod and be press-fitted into the mounting hole to obtain high friction between the tie rod and the sleeve. This prevents the tie rod from moving at high speed into the engine compartment through the mounting hole in the corresponding engine component if it breaks.

[0021] The sleeve is preferably rotationally symmetrical in order to provide sufficient grip on the tie rod to which it is attached.

[0022] Furthermore, it is preferable that the sleeve has an annular collar at the end facing the nut, having a lower side that contacts the engine component and an upper side that faces the nut. It is preferable to place a washer between the nut and the sleeve. In some embodiments, two tie rods are mounted adjacent to each other in their respective mounting holes, and a common double washer is used for both tie rods, the double washer being positioned between the nut and the sleeve of each of the two tie rods. In this preferred embodiment, if one tie rod breaks, the double washer and therefore the two sleeves in each mounting hole are held in place by at least one nut.

[0023] The annular collar of the sleeve may be countersinked into the upper surface of the engine component by recessing the upper surface of the engine component. Thus, the annular collar fits snugly onto the upper surface of the engine component, yet it is still easily removable.

[0024] The washer placed on the sleeve can be fixed to the engine component with bolts or screws, or it can be fixed by welding or other fastening means.

[0025] The tie rod may have a diameter greater than the inner diameter of the sleeve positioned in the mounting hole on the side opposite the mounting hole relative to the nut. This effectively prevents the tie rod from moving upward through the mounting hole if it breaks. In such an embodiment, the tie rod has a first portion having a first diameter which is the portion that passes through the mounting hole, and a second portion having a larger diameter than the first portion, and preferably the tie rod further has a conical portion between the first portion and the second portion.

[0026] More preferably, in the sleeve, at least a part of the end portion opposite to the end portion facing the nut is provided with a plurality of slits extending in the longitudinal direction, whereby the end portion is divided into a plurality of segments. When the tie rod breaks and the tie rod moves into the mounting hole, the plurality of segments are radially pressed toward the mounting hole. Thereby, the frictional force between the sleeve and the corresponding tie rod gradually increases, and the tie rod is effectively braked. In this embodiment, the sleeve may have a thin material thickness over a short section. This is to facilitate the radial movement of the segment.

[0027] Furthermore, the mounting hole may have a conical portion at the end portion opposite to the end portion facing the nut. Thereby, the contact area between the tie rod and the sleeve can be increased. The conical portion of the mounting hole is preferably in a shape that is essentially complementary to the conical portion between the first portion and the second portion of the tie rod. Thereby, effective braking of the tie rod at the time of breakage is realized.

[0028] In order to facilitate the attachment of the sleeve to the tie rod having a larger diameter on both sides of the attachment hole, the sleeve is preferably configured to be divided into at least two parts in the longitudinal direction of the sleeve.

[0029] According to an embodiment, the preload bolt assembly may be a hydraulic preload bolt assembly.

Brief Description of the Drawings

[0030] Hereinafter, the present invention will be described in more detail while referring to the exemplary embodiments shown in the drawings. [Figure 1] It is a view showing an overview of a large two-stroke diesel engine according to an exemplary embodiment as seen from the front direction. [Figure 2] It shows an overview of the large two-stroke engine of FIG. 1 as seen from the back direction. [Figure 3]Figure 1 is a schematic representation of a large two-stroke engine. [Figure 4] This is a side view of a first embodiment of the preloaded bolt assembly according to the present invention. [Figure 5] This is a side view of a second embodiment of the preloaded bolt assembly according to the present invention. Detailed description

[0031] In the following detailed description, the present invention will be described in relation to a large turbocharged two-stroke crosshead internal combustion engine. However, it should be noted that in some embodiments, the internal combustion engine may be of a different type. The illustrated large turbocharged two-stroke uniflow crosshead internal combustion engine is a dual-fuel engine and is of the high-pressure type. That is, fuel is injected at or near top dead center of the piston and ignited by compression. However, typically, pilot ignition using an igniter, such as fuel oil, is also used to ensure reliable ignition.

[0032] Figures 1-3 depict a turbocharged large low-speed two-stroke diesel engine. This engine has a crankshaft 8 and a crosshead 9. Figure 3 is a schematic representation of the turbocharged large low-speed two-stroke diesel engine, along with its intake and exhaust systems. In this embodiment, the engine has six cylinders in series. A turbocharged large low-speed two-stroke diesel engine typically has 4 to 14 cylinders arranged in series. These cylinders are supported on a cylinder block 23. The cylinder block 23 is supported on an engine frame 11 and a bed plate 24. Such an engine can be used, for example, as a main engine in a ship or as a stationary engine to power a generator in a power plant. The total output of the engine can be in the range of, for example, 1,000 to 110,000 kW.

[0033] The engine of this embodiment is a two-stroke uniflow compression-ignition dual-fuel engine. Each cylinder liner 1 is provided with a scavenging port 18 in its lower region and an exhaust valve located in the center of its top. In the illustrated embodiment, the engine has at least one mode in which it is operated with an alternative fuel and at least one conventional fuel mode in which it is operated with a conventional fuel such as fuel oil (marine diesel fuel) or heavy oil.

[0034] Scavenging air is introduced through the scavenging receiver 2 to the scavenging port 18 of each cylinder 1. The piston 10 reciprocates between bottom dead center (BDC) and top dead center (TDC) in the cylinder liner 1, compressing the scavenging air. Fuel (fuel oil in fuel oil mode, alternative fuel in alternative fuel mode) is injected into the combustion chamber in the cylinder liner 1 at or near TDC through a plurality of high-pressure fuel valves 50 located in the cylinder cover 22. Combustion occurs, and exhaust gas is produced. In the illustrated embodiment, each cylinder cover 22 is equipped with two fuel valves 50, but there may be more fuel valves 50. The fuel valves 50 are configured to inject only one specific type of fuel. For this reason, some of the fuel valves 50 are configured to inject alternative fuel, and some are configured to inject conventional fuel in the form of fuel oil into the combustion chamber. Thus, the engine may have two or more fuel valves 50. The fuel valve 50 is positioned in the cylinder cover 22, around the exhaust valve 4 located in the center of the cylinder cover 22. Ignition is timed at or near TDC. Ignition is achieved by a spark, laser, injection of igniter, etc. Although not shown, in some embodiments, an additional (usually small) fuel valve may be provided in the cylinder cover, configured to inject igniter to ensure ignition of an alternative fuel. The igniter is conventional diesel fuel, but may be other forms of ignition accelerators, such as dimethyl ether (DME) or hydrogen. Since the engine is a dual-fuel engine, it is equipped with a conventional fuel supply system (not shown) for supplying conventional fuel to the fuel valve 50. In some embodiments, this primary fuel injection system may also be used for the purpose of ensuring ignition of ammonia fuel.

[0035] When the exhaust valve 4 opens, the exhaust flows through the exhaust duct provided in the cylinder 1 to the exhaust receiver 3, then through the selective catalytic reduction reactor (SCR reactor) 28, through the first exhaust pipe 19, and to the turbine 6 of the turbocharger 5. From there, the exhaust flows through the second exhaust pipe 25 to the economizer 20, and is then released into the atmosphere from the outlet 21. The SCR reactor reduces NOx emissions.

[0036] The turbine 6 drives the compressor 7 via a shaft. The compressor 9 is supplied with outside air through the air intake 12. The compressor 7 sends the compressed scavenging air to the scavenging pipe 13, which is connected to the scavenging receiver 2. The scavenging air in the scavenging pipe 13 passes through the intercooler 14 to cool the scavenging air.

[0037] The cooled scavenging air passes through an auxiliary blower 16 driven by an electric motor 17. The auxiliary blower 16 compresses the scavenging airflow when the compressor 7 of the turbocharger 5 cannot provide sufficient pressure for the scavenging tank 2, i.e., when the engine is under low or partial load. When the engine is under high load, the compressor 7 of the turbocharger can supply sufficiently compressed scavenging air, so the auxiliary blower 16 is bypassed by a check valve 15 and the electric motor 17 is stopped.

[0038] In the large two-stroke engines of the type described above, various engine components are secured together by a preload bolt assembly. In the conventional large two-stroke engines of the type described above, the cylinder cover 22 is secured to the cylinder block 23 by a first set of tie rods 40 (see Figure 4). Each tie rod has one end threaded and is screwed into a corresponding threaded hole in the cylinder block 23. The other end passes through a mounting hole 41 in the cylinder cover 22 and is secured by a nut 42 screwed into the threads of the tie rod 40, thereby securing the cylinder liner 1 in place. Another set of tie rods (not shown) extends from the underside of the bed plate 24 to the topside of the cylinder block 23, securing the engine block 23, engine frame 11, and bed plate 24 together.

[0039] During the combustion period in the cylinder, when the injected fuel burns, a downward force acts on the piston 10, while an equivalent upward force acts on the cylinder cover 22, which is transmitted through the cylinder block 23 and engine frame 11 to the bed plate 24.

[0040] All tie rods 40 are pre-loaded during engine assembly so that they can absorb these enormous forces acting on the cylinder cover 22, cylinder block 23, and bed plate 24, especially during the combustion period in the cylinder. Therefore, the tie rods 40 have internal forces as tensile stress. Consequently, if a tie rod 40 breaks for any reason, it could fly upward and into the engine compartment, potentially causing serious damage to personnel inside the engine compartment or to the engine itself.

[0041] According to the present invention, the preload bolt assembly is provided with a braking means 43 that encircles at least some of the tie rods 40. This prevents the tie rod 40 having the braking means 43 from moving through the mounting hole of the engine component in the event of breakage. In the example in Figure 4, this engine component is comprised of a cylinder cover 22, and in the example in Figure 5, it is comprised of a cylinder block 23.

[0042] Therefore, even if the tie rod 40 breaks, it is prevented from flying upward through the mounting holes of the engine parts 22 and 23 and into the engine room.

[0043] In the example of the first embodiment of the present invention shown in Figure 4, the brake means 43 is positioned on the opposite side of the mounting hole from the nut 42. The brake means 43 has a radial dimension larger than the mounting hole 41, at least in part thereof.

[0044] The illustrated braking means 43 is provided in the form of a bushing 45. The bushing 45 is rotationally symmetrical to ensure sufficient grip on the corresponding tie rod 40. Furthermore, the illustrated bushing 45 is formed to have a conical outer surface 46 at the end facing the mounting hole 41 formed in the cylinder cover 22. The diameter of the conical outer surface 46 is smallest at the end facing the mounting hole 41. Since the minimum diameter of this conical outer surface 46 is smaller than the diameter of the mounting hole 41 in the cylinder cover 22, the bushing can move at least a certain distance within the mounting hole 41 in the cylinder cover 22 if the corresponding tie rod 40 is damaged.

[0045] The bushing 45 has a conical outer surface 46 at its end, which is provided with multiple longitudinally extending slits 47. Therefore, the end with the conical outer surface 46 is divided into multiple segments 48. If the tie rod 40 that passes through the bushing 45 breaks and the bushing 45 is pushed into the mounting hole 41, the multiple segments 48 may be crushed radially toward the tie rod 40.

[0046] This method gradually increases the frictional force between the bushing 45 and the corresponding tie rod 40, effectively braking the tie rod 40 and preventing it from popping out of the mounting hole 41.

[0047] The illustrated bushing 45 is divided into two parts along its longitudinal direction, as shown in the sketch on the right of Figure 4, so that the bushing can be easily installed on the tie rod without disassembling the engine.

[0048] In the illustrated embodiment, the bushing 45 is held in place by a hose clamp 49. The hose clamp 49 is attached to the tie rod 40 just below the bushing 45 and supports the bushing.

[0049] The bushing 45 is preferably formed from a suitable steel material.

[0050] In the second embodiment of the invention shown in Figure 5, the brake means 43 is located within the mounting hole 41. In this embodiment, the brake means 43 is provided in the form of a sleeve 60 having an annular collar 61 at the end facing the nut. In the illustrated embodiment, the sleeve is loosely mounted in the mounting hole 41, with a small clearance between the mounting hole 41 and the sleeve 60.

[0051] When assembled, the annular collar 61 has its lower side 62 in contact with the cylinder block 23 and its upper side 63 facing the nut 42. As shown in the figure, two tie rods 40 are mounted adjacent to each other in the mounting holes 41. A double washer 64 is positioned between the two nuts 42 and the two sleeves 60. In this embodiment, even if one of the tie rods 40 is damaged, the double washer 64 and the two sleeves 60 in each mounting hole 41 are held in place by at least one nut 42. Figure 5 shows the right tie rod 40 damaged, with the right tie rod 40 moved slightly upward in the mounting hole 41.

[0052] As shown in the figure, the tie rod 40 has a diameter greater than the inner diameter of the sleeve 60 positioned in the mounting hole 41, on the opposite side of the mounting hole 41 from the nut 42. This effectively prevents the tie rod 40 from moving upward through the mounting hole 41 even if the tie rod 40 is damaged. In such an embodiment, the tie rod 40 has a first portion 40a having a first diameter which is the portion that passes through the mounting hole 41, and a second portion 40b having a diameter greater than the first diameter. The tie rod 40 further includes a conical portion 40c between the first portion 40a and the second portion 40b of the tie rod 40.

[0053] The sleeve 60 is provided with a plurality of longitudinally extending slits 65 that open at the end facing the nut 42 and at the end opposite, thereby dividing the end into a plurality of corresponding segments 66. If the tie rod 40, which is passed through the sleeve 60, breaks and the tie rod 40 moves through the mounting hole 41 in the cylinder block 23, the plurality of segments 66 can be pressed radially toward the wall of the mounting hole 41. In this manner, the frictional force between the sleeve 60 and the corresponding tie rod 40 gradually increases, effectively braking the tie rod 40. As shown in the figure, in this embodiment, the thickness of the material of the sleeve is reduced in a short section 60a. This is to facilitate the radial movement of the segments 66.

[0054] Furthermore, the mounting hole 41 has a conical portion 67 at the end opposite to the end facing the nut 42. This increases the contact area between the tie rod 40 and the sleeve 60 in the event of breakage. The conical portion 60 of the mounting hole 41 is essentially complementary in shape to the conical portion 40c between the first and second parts of the tie rod 40, thus enabling effective braking of the tie rod 40 in the event of fracture.

[0055] In order to allow the sleeve to be easily attached to the tie rod 40, which has a larger diameter on both sides of the mounting hole 41, the sleeve 60 is configured to be divided into two parts in the longitudinal direction of the sleeve 60.

Claims

1. A preload bolt assembly for connecting at least two engine components of a large turbocharged two-stroke uniflow crosshead internal combustion engine, The preload bolt assembly comprises at least one tie rod having threads at its end and at least one nut for securing one of the at least two engine components to the other of the at least two engine components. The at least two engine components are connected by the at least one tie rod and the at least one nut, and each of the at least one tie rod has at least one end passing through a mounting hole in at least one of the at least two engine components. The at least one nut is screwed into the threads of the at least one tie rod at one end of the mounting hole. The preload bolt assembly is characterized by comprising a braking means disposed on the outer circumference of at least one of the at least one tie rods, and in the event of failure of the tie rod equipped with the braking means, the tie rod is prevented from moving through the mounting hole. Preloaded bolt assembly.

2. The preload bolt assembly according to claim 1, wherein each of the braking means is positioned on the opposite side of the mounting hole from the nut and has a radial dimension larger than the mounting hole in at least a portion of it.

3. The preload bolt assembly according to claim 1, wherein the braking means is provided in the form of a bushing.

4. The preload bolt assembly according to claim 3, wherein the bushing is formed to have a conical outer surface at least at the end facing the mounting hole, the diameter of the conical outer surface is smallest at the end facing the mounting hole, and the smallest diameter of the conical outer surface is smaller than the diameter of the mounting hole.

5. The preload bolt assembly according to claim 4, wherein at least a portion of the bushing has a plurality of longitudinally extending slits at the end having the conical outer surface, the end having the conical outer surface is divided into a plurality of segments, and when the tie rod through which the bushing passes breaks and the bushing is pushed into the mounting hole of the engine component, the plurality of segments can be crushed radially toward the tie rod.

6. The preload bolt assembly according to claim 3, wherein the bushing is held in a predetermined position by a hose clamp, and the hose clamp is attached to the tie rod at a position immediately below the bushing and supports the bushing.

7. The preload bolt assembly according to claim 1, wherein the braking means is disposed within the mounting hole.

8. The preload bolt assembly according to claim 7, wherein the braking means is provided in the form of a sleeve.

9. The preload bolt assembly according to claim 8, wherein the sleeve is provided with an annular collar at the end facing the nut, having a lower side that contacts the engine component and an upper side that faces the nut.

10. The preload bolt assembly according to claim 8, wherein a washer is disposed between the nut and the sleeve.

11. The preload bolt assembly according to claim 8, wherein two tie rods are mounted adjacent to each other in their respective mounting holes, a double washer common to the two tie rods is used, and the double washer is positioned between the nut and the sleeve of each of the two tie rods.

12. The preload bolt assembly according to claim 8, wherein the tie rod has a diameter on the opposite side of the mounting hole from the nut that is larger than the inner diameter of the sleeve positioned in the mounting hole.

13. The preload bolt assembly according to claim 12, wherein the tie rod has a first portion having a first diameter which is the portion that passes through the mounting hole, a second portion having a diameter larger than the first diameter, and a conical portion between the first portion and the second portion.

14. The preload bolt assembly according to claim 8, wherein the sleeve is provided with a plurality of longitudinal slits in at least a portion of the end opposite to the end facing the nut, thereby dividing the opposite end into a corresponding number of segments.

15. The preload bolt assembly according to claim 7, wherein a conical portion is provided in the mounting hole at the end opposite to the end facing the nut.

16. A large turbocharged two-stroke uniflow crosshead internal combustion engine comprising a preload bolt assembly as described in any one of claims 1 to 15.

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