Longitudinally scavenging large-sized diesel engine

Abstract

To provide a large-sized diesel engine capable of simply adjusting a compression ratio.SOLUTION: A large-sized diesel engine has at least one cylinder 2 that has a combustion chamber 4 limited by a piston 3 capable of reciprocating along a cylinder axis A, and a rotatable crank shaft 9. The piston is connected to a cross head 7 having a cross head pin 71 through a piston rod 6, and the cross head is connected to a crank shaft through a push rod 8. The piston rod 6 is located in the cross head pin and is provided with a control device 10 for adjusting a compression ratio, so that the piston rod can move in a direction of the cylinder axis A with respect to the cross head pin. The piston rod has a lower part 61 in the cross head pin and an upper part 62 connecting the piston to the lower part, and the lower part and the upper part are detachably connected with each other.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a large diesel engine according to the preamble of the independent claim. [Background technology]

[0002] Large diesel engines traditionally run on heavy fuel oil. They can be designed as two-stroke or four-stroke engines, e.g., longitudinally scavenged two-stroke large diesel engines. They are frequently used as propulsion units for ships or in stationary operation, for example, to power large generators for electrical energy generation. In this process, the engines typically operate continuously for long periods of time, which places considerable demands on operational safety and availability. Therefore, particularly long maintenance intervals, low wear, and economical use of operating materials are key criteria for operators. Large diesel engines typically have cylinders with an internal diameter (bore) of at least 200 mm. Today, large diesel engines with bores up to 960 mm or even larger are in use.

[0003] Due to the need for economical and efficient operation, compliance with emission standards, and resource conservation, alternatives to heavy fuel oil are now being sought in large diesel engines. Therefore, both liquid fuels, which are fuels introduced into the combustion chamber in liquid form, and gaseous fuels, which are fuels introduced into the combustion chamber in gaseous form, are used.

[0004] Examples of liquid fuels known as substitutes for heavy oil include other heavy hydrocarbons, alcohols, especially methanol or ethanol, gasoline, diesel, or emulsions or suspensions, which remain as residues during the refining of heavy oil. For example, the use of emulsions called multiphase superfine atomized residue (MSAR) as fuel is known. Known suspensions are made from a suspension of coal dust and water and are also used as fuel for large engines. Known gaseous fuels include natural gases, such as liquefied natural gas (LNG), liquid gases, such as liquefied petroleum gas (LPG), or ethane.

[0005] Also known are, in particular, large diesel engines which can be operated using at least two different fuels, the engine being operated using one fuel or the other depending on the operating situation or operating environment.

[0006] One example of a heavy-duty diesel engine that can operate using two different fuels is a heavy-duty diesel engine designed as a dual-fuel heavy-duty diesel engine, which can operate in a liquid mode, where liquid fuel is introduced into the cylinder and burned, and in a gas mode, where gas is introduced into the cylinder as fuel.

[0007] Heavy-duty diesel engines can operate using at least two different liquid or gaseous fuels and often operate in different modes depending on the fuel actually being used. In what is often called diesel operation, fuel combustion generally follows the principles of compression ignition or autoignition. In what is often called Otto operation, combustion is triggered by spark ignition of an ignitable premixed air-fuel mixture. This spark ignition can be triggered by an electrical spark, for example from a spark plug, or by a small amount of injected fuel self-igniting and thereby triggering the spark ignition of another fuel. Here, a small amount of fuel intended to self-ignite is often injected into a pre-combustion chamber connected to the combustion chamber.

[0008] Furthermore, mixed forms of Otto and Diesel operation are also known.

[0009] Within the scope of this application, the term "heavy-duty diesel engine" refers to an engine that is capable of operating at least in diesel operation. In particular, the term "heavy-duty diesel engine" also includes large dual-fuel engines that are capable of operating in other operating modes in addition to diesel operation, such as Otto operation.

[0010] Within the scope of this application, the term "gas mode," or in other words, "operating in gas mode," refers to the use of only gas or gaseous fuel as the fuel for torque-producing combustion. As noted above, to spark-ignite a premixed air-fuel mixture in gas mode, it is possible, and quite common, to inject small amounts of auto-ignitable liquid fuel, such as heavy fuel oil, to trigger spark ignition, but even so, the torque-producing combustion process is fueled exclusively by gas or gaseous fuel.

[0011] This process of spark ignition via the autoignition of a small amount of liquid fuel is sometimes called pilot injection. This pilot injection has nothing to do with the injection of liquid fuel into the combustion chamber when operating a large engine in liquid mode. Pilot injection typically uses a different injection mechanism than the injection of liquid fuel in liquid mode. Also, during pilot injection, the small amount of liquid fuel is not injected directly into the combustion chamber, but is often injected into at least one pre-combustion chamber connected to the combustion chamber via a duct.

[0012] It is also known to operate such large dual-fuel diesel engines in gas mode using a low-pressure method, i.e., gas is introduced into the cylinder in a gaseous state at a gas injection pressure of up to 50 bar, preferably up to 20 bar. For this purpose, at least one gas inlet is provided in the cylinder wall, through which gas is introduced in gas mode. In practice, two gas inlets are often provided, located diametrically opposite each other relative to the cylinder axis. Here, the gas inlets are located at a height between the lower and upper reversal points of the piston movement, at which gas can be introduced into the cylinder during its upward movement, as long as no compression, or at least no substantial compression, has occurred in the cylinder.

[0013] Typically, heavy-duty diesel engines are designed so that at 100% load, i.e. at full load, the densification ratio, or in other words the compression ratio, is optimized, and therefore the heavy-duty diesel engine achieves the best possible compromise between consumption behavior and efficiency coefficient at 100% load, which means that the heavy-duty diesel engine is designed to have the highest possible thermodynamic efficiency coefficient at 100% load, i.e. at full load and maximum rotational speed.

[0014] The compression ratio is a geometric value that is the ratio of a first volume of the combustion chamber before compression of the air-fuel mixture to a second volume remaining in the combustion chamber after compression of the air-fuel mixture.

[0015] By optimizing the combustion behavior at 100% load, the efficiency coefficient of large diesel engines is consequently not optimal at lower loads, e.g. low and medium pressures.

[0016] Furthermore, in large diesel engines that are operated on at least two different fuels, for example, dual-fuel large diesel engines, it is desirable to achieve the highest possible efficiency coefficient for each of the different fuels.

[0017] For these reasons, large diesel engines are known in which the compression ratio can be varied to optimize the efficiency factor for each load and / or each fuel, such designs are also called VCR systems (Variable Compression Rate).

[0018] From EP-A-2 687 707 it is known, for example, to change the compression ratio in a large diesel engine with crosshead drive, by moving the piston rod, which is supported in the crosshead pin of the crosshead, in the direction of the cylinder axis relative to the crosshead pin. In this way, the compression ratio can be changed. For example, by moving the piston rod in the direction of the combustion chamber relative to the crosshead pin, the volume of the combustion chamber at maximum compression becomes smaller and therefore the compression ratio becomes higher. [Prior art documents] [Patent documents]

[0019] [Patent Document 1] European Patent Application Publication No. 2687707 Summary of the Invention [Problem to be solved by the invention]

[0020] Based on this state of the art, the object of the present invention is to propose a large diesel engine with crosshead drive, in which the compression ratio can be easily adjusted, and in which a particularly advantageous and economical embodiment for changing the compression ratio is provided. [Means for solving the problem]

[0021] The subject matter of the invention which achieves this object is characterized by the characterizing parts of the independent patent claims.

[0022] According to the present invention, a large diesel engine is proposed, which includes at least one cylinder having a combustion chamber defined by a piston positioned so as to be reciprocally movable along the cylinder axis, a rotatable crankshaft, the piston connected via a piston rod to a crosshead having a crosshead pin, the crosshead connected to the crankshaft via a push rod, the piston rod located in the crosshead pin, and a control device for adjusting the compression ratio, by means of which the piston rod is movable in the direction of the cylinder axis relative to the crosshead pin. The piston rod has a lower part and an upper part, the lower part located in the crosshead pin, the upper part connecting the piston to the lower part, and the lower and upper parts being detachably connected to each other.

[0023] This embodiment of the piston rod with a lower and upper portion represents a particularly advantageous and economical embodiment that allows the compression ratio in the cylinder to be varied.

[0024] Thus, for example, the lower part of the piston rod, which is located within the crosshead pin and is subjected to more strain during operation, can be made of higher quality material and / or with higher precision than the upper part of the piston rod, which can be made from cheaper material and / or with lower requirements in terms of precision.

[0025] This embodiment is also advantageous in terms of maintenance or service work: for example, if the piston and piston rod are to be removed from the cylinder in a maintenance situation, the embodiment according to the invention allows the piston to be pulled out of the cylinder together with the upper part of the piston rod, while the lower part of the piston rod remains in the crosshead pin. The lower part, which remains in the crosshead, is therefore significantly better protected.

[0026] The embodiment of the piston rod with a lower and upper part is also very advantageous in terms of manufacturing. The machining of the lower part is significantly easier. For example, the bores in the lower part, which are required for the supply and discharge of cooling oil that is guided through the piston rod to the piston during the operating mode, can therefore be manufactured much more easily, i.e., directly from the upper side of the lower part. This no longer has to be done from the upper end of the piston rod, i.e., the end connected to the piston.

[0027] Additionally, because the lower section can be manufactured separately from the rest of the piston rod, the overall machining of the lower section is significantly easier. The lower section must accommodate the crosshead pin of the crosshead, which typically requires much higher precision, which is much easier to achieve by manufacturing the lower section separately. Because the lower section can be manufactured and machined separately from the rest of the piston rod, other processing steps on the lower section, such as grinding, surface treatments such as surface hardening, surface coating with, for example, chromium, surface coating via PVD (Physical Vapor Deposition), surface coating via weld cladding, or heat treatment, are also significantly easier to perform.

[0028] Preferably, the lower part of the piston rod is designed as a hydraulic piston that defines a hydraulic chamber located within the crosshead pin. Therefore, the control device for adjusting the compression ratio is designed as a hydraulic device. By introducing a hydraulic medium, such as oil, into the hydraulic chamber inside the crosshead pin, the piston rod can be moved axially relative to the crosshead pin via the lower part designed as a hydraulic piston, thereby decreasing the minimum volume of the combustion chamber. By draining the hydraulic medium from the hydraulic chamber, the piston rod can be lowered relative to the crosshead pin, thereby increasing the minimum volume of the combustion chamber.

[0029] A major advantage, especially when the lower part of the piston rod is designed as a hydraulic piston, is that it can be separated from the upper part and therefore manufactured separately. This makes it much easier to meet the high requirements for precision design of the hydraulic piston. Here too, it is advantageous that the lower part, designed as a hydraulic piston, remains protected in the crosshead pin during maintenance work, when the rest of the piston rod, together with the piston, is extracted from the cylinder.

[0030] Particularly preferably, the lower section is made of a first material and the upper section is made of a second material, the first material being different from the second material. The first material is preferably a highly robust material that can withstand large mechanical strains, especially when the lower section is provided with bores for, for example, cooling oil, lubricating oil, or other fluids. The second material is preferably a cheaper material, such as steel, which reduces manufacturing costs. Of course, embodiments are also possible in which the first material is the same as the second material, i.e., the lower and upper sections of the piston rod are made of the same material.

[0031] According to a preferred embodiment, the lower portion has a first length in the axial direction of the cylinder and the upper portion has a second length in the axial direction of the cylinder, the second length being at least three times, preferably at least five times, the first length, thereby making it possible to manufacture the main part of the piston rod more cheaply by minimizing the size of the lower portion, which is usually made of more expensive material or subjected to additional processing.

[0032] Preferably, the interface between the lower and upper portions of the piston rod is positioned such that the lower portion of the piston rod always remains below the sealing arrangement, which seals the piston rod's path into the cylinder, during operation of the heavy-duty diesel engine. Typically, the piston rod's path into the cylinder of a heavy-duty diesel engine is sealed by a stuffing box. The interface between the lower and upper portions of the piston rod is then positioned such that the interface does not pass through the stuffing box and always remains below the stuffing box during the working movement of the piston.

[0033] Below we will list some more preferable ways to design the lower and upper parts of the piston rod.

[0034] Preferably, the lower portion of the piston rod has an upper end that is connected to the lower end of the upper portion of the piston rod.

[0035] According to a preferred embodiment, the upper end of the lower portion of the piston rod has a larger outer diameter than the lower end of the upper portion of the piston rod.

[0036] In another preferred embodiment, the upper end of the lower section of the piston rod has the same outer diameter as the lower end of the upper section of the piston rod.

[0037] In some embodiments, the upper end of the lower portion of the piston rod has a smaller outer diameter than the lower end of the upper portion of the piston rod.

[0038] Furthermore, in a preferred embodiment, the upper end of the lower portion of the piston rod has a recess that receives the lower end of the upper portion of the piston rod.

[0039] In this embodiment, it is particularly preferred that the upper end of the lower portion of the piston rod completely surrounds the lower end of the upper portion.

[0040] According to another preferred embodiment, the lower end of the upper portion of the piston rod has a socket that receives the upper end of the lower portion of the piston rod.

[0041] In this embodiment, it is particularly preferred that the lower end of the upper portion of the piston rod completely surrounds the upper end of the lower portion.

[0042] Since the lower portion of the piston rod is subjected to the strongest mechanical strains during the operating conditions of a large diesel engine, the manufacture of the lower portion preferably includes surface hardening.

[0043] Preferably, the heavy-duty diesel engine is designed as a longitudinally scavenged two-stroke heavy-duty diesel engine.

[0044] It is particularly preferred that the heavy-duty diesel engine be designed as a dual-fuel heavy-duty diesel engine capable of operating in a liquid mode in which a liquid fuel is introduced into the combustion chamber and burned, and further capable of operating in a gas mode in which a gas is introduced into the combustion chamber and burned.

[0045] Further advantageous measures and embodiments of the invention result from the dependent claims.

[0046] The present invention will be described in more detail below with reference to examples and drawings. [Brief explanation of the drawings]

[0047] [Figure 1] 1 is a schematic cross-sectional view of one embodiment of a large diesel engine according to the present invention. [Figure 2]1 is a schematic cross-sectional view of one embodiment of a piston rod. [Figure 3] 3 is a view similar to FIG. 2, but with the lower portion shown separated from the upper portion. [Figure 4] Similar to Figure 2, but for a different variant of piston rod design. [Figure 5] Similar to Figure 2, but for a different variant of piston rod design. [Figure 6] Similar to Figure 2, but for a different variant of piston rod design. [Figure 7] Similar to Figure 2, but for a different variant of piston rod design. [Figure 8] Similar to Figure 2, but for a different variant of piston rod design. [Figure 9] Similar to Figure 2, but for a different variant of piston rod design. DETAILED DESCRIPTION OF THE INVENTION

[0048] The term "large diesel engine" usually refers to an engine used as the main drive unit of a ship or also in stationary operation, for example to power large generators for generating electrical energy. Typically, the cylinders of a large diesel engine each have an internal diameter (bore) of at least about 200 mm. The term "longitudinal scavenging" refers to the fact that scavenging air or charge air is introduced into the cylinder in the region of its lower end. Combustion residues, especially exhaust gases, are discharged from the upper end of the cylinder.

[0049] The following description of the present invention refers to a heavy-duty diesel engine designed as a dual-fuel engine, i.e., an engine capable of operating using two different fuels. Specifically, a dual-fuel heavy-duty diesel engine can be operated in liquid mode, in which only liquid fuel is injected into the combustion chamber of a cylinder. Typically, a liquid fuel, such as heavy fuel oil or diesel oil, is injected directly into the combustion chamber at the appropriate moment and self-ignites according to the diesel principle of autoignition. A heavy-duty diesel engine can also be operated in gas mode, in which a gas, such as natural gas (e.g., liquefied natural gas (LNG)) or liquefied petroleum gas (LPG) or ethane, serves as fuel and is burned in the combustion chamber via spark ignition in the form of a premixed air-fuel mixture.

[0050] As already mentioned above, within the scope of the present application, the term "gas mode", or in other words "operation in gas mode", is to be understood as meaning that in this gas mode, a large diesel engine is operated using only gas or gaseous fuel, optionally with a small amount of auto-ignition fuel, such as heavy fuel oil or diesel oil, being introduced into the combustion chamber or pre-chamber or pre-chambers solely for spark ignition of the air-gas mixture (pilot injection).

[0051] Specifically, in gas mode, large diesel engines operate according to the low-pressure method, i.e., gas is introduced into the cylinder in gaseous state at an injection pressure of up to 50 bar, preferably up to 20 bar. The air-gas mixture is spark-ignited in the combustion chamber according to Otto's principle. This spark-ignition is preferably triggered by introducing a small amount of self-igniting liquid fuel (e.g., diesel or heavy fuel oil) into the combustion chamber or pre-chamber or pre-chambers at the right moment, which self-ignites and causes spark-ignition of the air-fuel mixture in the combustion chamber.

[0052] In the embodiments described herein, reference is made to a heavy-duty diesel engine designed as a crosshead-driven, longitudinally scavenged, two-stroke, dual-fuel heavy-duty diesel engine. Naturally, the invention is not limited to dual-fuel heavy-duty diesel engines, but relates to all types of heavy-duty diesel engines, i.e., large engines that can at least be operated in diesel operation.

[0053] Figure 1 is a simplified schematic diagram of one embodiment of a large diesel engine according to the present invention, generally designated by the reference numeral 1. In Figure 1, only one cylinder 2 of the large diesel engine 1 is depicted, out of the usual multiple cylinders 2.

[0054] Inside the cylinder 2, a piston 3 is arranged in a manner known per se and is positioned so as to be reciprocatable between a lower reversal point and an upper reversal point along the cylinder axis A. Figure 1 shows the piston 3 at the upper reversal point of its cyclical motion.

[0055] The piston 3 has an upper surface 31 which, in cooperation with the cylinder cover 21, defines a combustion chamber 4 within which the combustion process takes place.

[0056] As is known in crosshead drives, the pistons 3 are connected via piston rods 6 to a crosshead 7, which in turn is connected via push rods 8 to a crankshaft 9, so that the movement of the pistons 3 is transmitted via the piston rods 6, the crosshead 7 and the push rods 8 to the crankshaft 9, causing it to rotate. The crosshead 7 is designed in a manner known per se to convert the linear up and down movement of the pistons 3 and piston rods 6 into a rotary movement of the push rods 8, which are pivotally mounted about crosshead pins 71 of the crosshead 7.

[0057] At the lower end of the cylinder 2 in the figure, a seal arrangement 22 is provided to seal the passage of the piston rod 6 into the cylinder 2. The seal arrangement 22 preferably includes a stuffing box.

[0058] The set-up and individual components of a heavy-duty diesel engine 1, such as the injection system for liquid mode (not shown), the gas supply system for gas mode (not shown), the gas exchange system, the exhaust system (not shown) or the turbocharging system for supplying scavenging air or intake air (not shown), as well as the control system and open-loop control system (not shown) of such a heavy-duty diesel engine 1, both in its embodiment as a two-stroke engine and in its embodiment as a four-stroke engine, are well known to the expert and do not require further explanation here.

[0059] 1 depicts only one of these components, outlet valve 5, as this is sufficient for understanding the present invention. A gas supply system for gas mode typically has two gas inlets (not shown) through which gas that serves as fuel in gas mode is introduced into cylinder 2. The two gas inlets are preferably located in the wall of cylinder 2, particularly preferably diametrically opposite each other, approximately midway between the upper and lower reversal points in the axial direction defined by cylinder axis A.

[0060] In modern heavy-duty diesel engines, the control system and open-loop control system are electronic systems through which all engine or cylinder functions, especially gas mode, are normally controlled. Injection (start and end of injection) in both the liquid and liquid modes, as well as the operation of the outlet valve 5, can be regulated or controlled or adjusted.

[0061] In the embodiment of a longitudinally scavenged two-stroke large diesel engine described herein, each cylinder 2 or cylinder liner typically has a scavenging slit (not shown) in the lower region thereof, which opens and closes periodically with the movement of the piston 3 in the cylinder 2, allowing scavenging air supplied by the turbocharger under charge pressure into an air intake receiver (not shown) to flow into the cylinder 2 as long as the scavenging slit is open. The cylinder head or cylinder cover 21 is typically provided with a centrally located outlet valve 5 through which the combustion gases can be discharged from the cylinder 2 after the combustion process into an exhaust system (not shown). The exhaust system directs at least a portion of the combustion gases to a turbocharger turbine (not shown), which in turn supplies charge air under charge pressure into the air intake receiver.

[0062] To introduce liquid fuel into the combustion chamber 4 of the cylinder 2 in liquid mode, one or more fuel injection nozzles (not shown) are provided, which are located, for example, in the cylinder cover 21 near the outlet valve 5. As liquid fuel in liquid mode, for example, heavy fuel oil or diesel oil can be burned.

[0063] For the gas supply in gas mode, or in other words for the introduction of gas, a gas supply system known per se is provided, which has gas inlets (not shown), each preferably designed as a gas inlet valve with a gas inlet nozzle.

[0064] The piston rod 6 is positioned so that its lower end in the figure is inside the crosshead pin 71. Furthermore, a control device 10 is provided for adjusting the compression ratio. The compression ratio is a geometric value that is the ratio of a first volume of the combustion chamber 4 before compressing the scavenging air or air-fuel mixture to a second volume remaining in the combustion chamber 4 after compressing the scavenging air or air-fuel mixture. The first volume is the volume of the combustion chamber 4 immediately after closing the outlet valve 5, i.e., at the start of compression as the piston 3 moves upward. The second volume is the volume of the combustion chamber 4 at maximum compression of the scavenging air or air-fuel mixture. This is essentially the volume of the combustion chamber 4 at the start of the combustion process.

[0065] Control devices 10 for varying the compression ratio are known from the state of the art, for example from the above-mentioned EP-A-2 687 707, and therefore do not require further explanation here.

[0066] In the large diesel engine 1 according to the invention, the control device 10 for adjusting the compression ratio is designed so that the entire piston rod 6, which is located inside the crosshead pin 71, can be moved relative to the crosshead pin 71 in the direction of the cylinder axis A. Thus, according to Figure 1, the piston rod 6, and therefore also the piston 3, can be moved upwards or downwards relative to the crosshead pin 71. If the piston rod 6 is moved upwards in the figure, the second volume, i.e. the volume at maximum compression, decreases, thereby increasing the compression ratio. If the piston rod 6 is moved downwards in the figure, the second volume, i.e. the volume at maximum compression, increases, thereby decreasing the compression ratio.

[0067] This allows the compression ratio to be optimally adjusted for each load at which the heavy-duty diesel engine 1 is operated, resulting in the most efficient possible combustion process for each load. Furthermore, dual-fuel heavy-duty diesel engines also allow the compression ratio to be optimally adjusted for each fuel in each case. For example, the heavy-duty diesel engine 1 can be operated with a lower compression ratio in gas mode than in liquid mode.

[0068] Furthermore, it is also possible to optimally adjust the compression ratio depending on other operating conditions or operating parameters, such as the temperature of the scavenging air (intake air), the methane number of the gas serving as fuel in gaseous mode, or other operating parameters.

[0069] According to the invention, the piston rod has a lower part 61 and an upper part 62, the lower part 61 being located in the crosshead pin 71 and the upper part 62 connecting the piston 3 to the lower part 61. The lower part 61 and the upper part 62 of the piston rod 6 are preferably detachably connected to each other by a number of bolts (not shown) which provide a threaded connection between the upper part 61 and the lower part 62, thereby firmly but detachably connecting the upper part 61 and the lower part 62. For this purpose, each bolt can engage in a threaded hole provided in the lower part 61 or the upper part 62, respectively.

[0070] According to a particularly preferred embodiment, the lower part 61 of the piston rod 6 is designed as a hydraulic piston, which defines a hydraulic chamber 11 of the control device 10. The hydraulic chamber 11 is arranged in the crosshead pin 71. Furthermore, not shown supply and discharge feeds with valves or locking mechanisms are provided, via which a hydraulic medium, e.g. oil, can be introduced into or discharged from the hydraulic chamber 11.

[0071] For example, if the compression ratio is to be increased, hydraulic medium is introduced into the hydraulic chamber 11, increasing the pressure in the hydraulic chamber 11. This increase in pressure in the hydraulic chamber 11 exerts an upward force on the lower part 61 of the piston rod 6, which is designed as a hydraulic piston, thereby moving the piston rod 6 and the piston 3 rigidly attached thereto upward.

[0072] When the compression ratio is to be reduced, the hydraulic medium is discharged from the hydraulic chamber 11 to reduce the pressure in the hydraulic chamber 11. This reduction in pressure in the hydraulic chamber 11 causes the piston rod 6 to move downward in the figure due to the force of its weight, thereby reducing the compression ratio.

[0073] In this way, the compression ratio can be continuously varied or adjusted hydraulically.

[0074] The embodiment of the piston rod 6 with a lower part 61 and an upper part 62 that are detachably connected to one another has the particular advantage that the lower part 61 and the upper part 62 can each be manufactured separately from one another, which makes it easily possible to make the lower part 61 from a first material and the upper part 62 from a second material that is different from the first material.

[0075] Therefore, a high quality material with very good mechanical properties such as high tensile strength, high toughness, elasticity, etc. can be selected for the lower part 61, which is subjected to much more severe mechanical strain than the upper part 62 during operation, while a cheaper material, such as steel, can be selected for the upper part 62, which is subjected to less strain.

[0076] Of course, there are also possible embodiments in which the lower portion 61 and the upper portion 62 are made of the same material, i.e., the first material is the same as the second material, and even in such embodiments, it is possible to machine the lower portion 61 with higher precision.

[0077] It is also possible in a simple manner to subject the lower part 61 to additional processing, such as surface hardening, for example via a laser, or heat treatment to improve the mechanical properties. Furthermore, it is possible to provide the lower part 61 in particular with a surface coating, for example with chromium, or via a PVD method, or via weld cladding.

[0078] It also becomes much easier to machine, e.g., grind, the lower part 61 as a separate component with high precision, which is particularly important when the lower part 1 is designed as a hydraulic piston that must seat very precisely in the hydraulic chamber 11.

[0079] Furthermore, it becomes significantly easier to carry out bore machining or other machining operations on the lower part 61 as a separate component. For example, bores can be made in the lower part 61 in a very simple manner, which bores serve to supply and discharge cooling oil to and from the interior of the piston rod 6.

[0080] The embodiment of the piston rod with the lower part 61 and the upper part 62 is also particularly advantageous in maintenance work. For example, in order to extract the piston 3 from the cylinder 2, it is possible to release the connection between the upper part 62 and the lower part 61. The piston 3 can then be removed from the cylinder 2 together with the upper part 62 of the piston rod 6, while the lower part 61 remains inside the crosshead pin 71 and is protected there. This is a very significant advantage, especially in the embodiment in which the lower part 61 is a hydraulic piston.

[0081] Preferably, the lower portion 61 of the piston rod 6 is designed to be significantly shorter than the upper portion 62 of the piston rod 6, since the lower portion 61 cooperates with the crosshead pin 71 and therefore typically requires much greater precision during manufacturing and / or is made of higher-quality material than the upper portion 62 of the piston rod 6. The lower portion 61 has a first length L1 ( FIG. 2 ) in the cylinder axial direction, and the upper portion 62 has a second length L2 in the cylinder axial direction. Preferably, the second length L2 is at least three times, more preferably at least five times, the first length L1. Particularly preferably, the lower portion 61 is designed with respect to its first length L1 such that, during operation of the large diesel engine, the lower portion 61 of the piston rod 6 always remains below the seal arrangement 22, which seals the passage of the piston rod 6 into the cylinder 2. In this way, it is possible to prevent the separation surface or separation area where the lower portion 61 and the upper portion 62 abut from passing through or entering the seal arrangement 22.

[0082] In the following, different variants of the embodiment of the piston rod 6 comprising an upper part 62 and a lower part 61 will be described with reference to FIGS.

[0083] Figure 2 shows in schematic cross section one embodiment of the piston rod 6, the same embodiment as that depicted in Figure 1. For better understanding, Figure 3 shows the embodiment of Figure 2 again, but with the lower part 61 depicted separately from the upper part 62.

[0084] The lower part 61 is designed essentially cylindrical and has an upper end 611 at which the lower part 61 meets the upper part 62. The upper part 62 has a cylindrical rod 622 and a lower end 621 that joins the rod 622 at the end face of the rod 622 facing the lower part 61. The upper part 62 meets the lower part 61 at the lower end 621.

[0085] The lower end 621 of the upper part 62 is also designed cylindrically and has an outer diameter D2 greater than the outer diameter D3 of the rod 622 of the upper part 62, so that the lower end 621 is designed as a kind of foot of the upper part 62.

[0086] The upper end 611 of the lower portion 61 of the piston rod 6 has an outer diameter D1 that is greater than the outer diameter D2 of the lower end 621 of the upper portion 62.

[0087] The upper end 611 of the lower part 61 has a centrally located recess 612 that is designed to receive the lower end 621 of the upper part 62. Preferably, the inner diameter of the recess 612 corresponds to the outer diameter D2 of the lower end 621 of the upper part 62, excluding any necessary clearances such as a loose fit or intermediate fit. This means that in this embodiment, the upper end 611 of the lower part 61 surrounds the lower end 621 of the upper part 62.

[0088] The variant of the embodiment of the piston rod 6 depicted in FIG. 4 largely corresponds to the embodiment depicted in FIGS. 2 and 3, but in the variant depicted in FIG. 4 the outer diameter D2 of the lower end 621 of the upper part 62 is equal to the outer diameter D3 of the rod 622 of the upper part 62.

[0089] 5, the lower end 621 of the upper portion 62 has a centrally located socket 623 that is designed to receive the upper end 611 of the lower portion 61. The upper end 611 of the lower portion 61 has an outer diameter D1 that is smaller than the outer diameter of the remainder of the lower portion 61, so that the upper end 611 forms a protrusion. Preferably, the inner diameter of the socket 623 corresponds to the outer diameter D1 of the upper end 611 of the lower portion 61, excluding any necessary clearances, such as a loose fit or intermediate fit. Thus, in this embodiment, the lower end 621 of the upper portion 62 surrounds the upper end 611 of the lower portion 61.

[0090] In figures 6 to 9, variants of the embodiment of the piston rod 6 are depicted, in which the separating surfaces on which the lower part 61 and the upper part 62 abut are in each case flat surfaces.

[0091] In the variant depicted in FIG. 6, the outer diameter D2 of the lower end 621 of the upper part 62 is greater than the outer diameter D3 of the rod 622 of the upper part 62 and is equal to the outer diameter D1 of the upper end 611 of the lower part 61 of the piston rod 6.

[0092] In the variant depicted in FIG. 7, the outer diameter D2 of the lower end 621 of the upper part 62 is equal to the outer diameter D3 of the rod 622 of the upper part 62 and is smaller than the outer diameter D1 of the upper end 611 of the lower part 61 of the piston rod 6.

[0093] In the variant depicted in FIG. 8, the outer diameter D2 of the lower end 621 of the upper part 62 is equal to the outer diameter D3 of the rod 622 of the upper part 62 and equal to the outer diameter D1 of the upper end 611 of the lower part 61 of the piston rod 6.

[0094] In the variant depicted in FIG. 9, the outer diameter D2 of the lower end 621 of the upper part 62 is equal to the outer diameter D3 of the rod 622 of the upper part 62 and is greater than the outer diameter D1 of the upper end 611 of the lower part 61 of the piston rod 6.

[0095] It will be appreciated that additional embodiments of the piston rod 6 with an upper portion 62 and a lower portion 61 are possible.

Claims

1. A large diesel engine having at least one cylinder (2) and a rotatable crankshaft (9), the at least one cylinder (2) having a combustion chamber (4) defined by a piston (3) arranged so as to be reciprocable along a cylinder axis (A), the piston (3) being connected via a piston rod (6) to a crosshead (7) having a crosshead pin (71), the crosshead (7) being connected to the crankshaft (9) via a push rod (8), the piston rod (6) being arranged in the crosshead pin (71), and a control device (10) for adjusting the compression ratio, the control device (10) allowing the piston rod (6) to be moved in the direction of the cylinder axis (A) relative to the crosshead pin (71).

1. A large diesel engine, comprising: a piston rod (6) having a lower portion (61) and an upper portion (62), the lower portion (61) being disposed within the crosshead pin (71), the upper portion (62) connecting the piston (3) to the lower portion (61), and the lower portion (61) and the upper portion (62) being detachably connected to each other.

2. 2. A large diesel engine according to claim 1, wherein the lower part (61) of the piston rod (6) is designed as a hydraulic piston which defines a hydraulic chamber (11) located in the crosshead pin (71).

3. 2. A large diesel engine according to claim 1, wherein said lower portion (61) is made from a first material and said upper portion (62) is made from a second material, said first material being different from said second material.

4. 2. A large diesel engine according to claim 1, wherein the lower portion (61) has a first length (L1) in the direction of the cylinder axis (A) and the upper portion (62) has a second length (L2) in the direction of the cylinder axis (A), the second length (L2) being at least three times, preferably at least five times, the first length (L1).

5. 2. A large diesel engine according to claim 1, characterized in that during operation of the large diesel engine, the lower portion (61) of the piston rod (6) is always below a sealing arrangement (22) sealing the path of the piston (6) into the cylinder (2).

6. 6. A large diesel engine according to any one of claims 1 to 5, wherein the lower part (61) of the piston rod (6) has an upper end (611) connected to a lower end (621) of the upper part (62) of the piston rod.

7. 7. A large diesel engine according to claim 6, wherein the upper end (611) of the lower portion (61) of the piston rod (6) has a larger outer diameter (D1) than the lower end (621) of the upper portion (62) of the piston rod (6).

8. 7. A large diesel engine according to claim 6, wherein the upper end (611) of the lower portion (61) of the piston rod (6) has the same outer diameter (D1) as the lower end (621) of the upper portion (62) of the piston rod (6).

9. 7. A large diesel engine according to claim 6, wherein the upper end (611) of the lower portion (61) of the piston rod (6) has a recess (612) that receives the lower end (621) of the upper portion (62) of the piston rod (6).

10. 10. A large diesel engine according to claim 9, wherein the upper end (611) of the lower portion (61) of the piston rod (6) completely surrounds the lower end (621) of the upper portion (62).

11. 7. A large diesel engine according to claim 6, wherein the lower end (621) of the upper portion (62) of the piston rod (6) has a socket (623) that receives the upper end (611) of the lower portion (61) of the piston rod (6).

12. 12. A large diesel engine according to claim 11, wherein the lower end (621) of the upper portion (62) of the piston rod (6) completely surrounds the upper end (611) of the lower portion (61).

13. 2. A large diesel engine according to claim 1, wherein the manufacturing process of said lower portion (61) includes surface hardening.

14. 2. A large diesel engine according to claim 1, designed as a longitudinally scavenged two-stroke large diesel engine.

15. 15. A heavy-duty diesel engine according to claim 14, designed as a dual-fuel heavy-duty diesel engine operable in a liquid mode in which liquid fuel is introduced into the combustion chamber for combustion, and further operable in a gas mode in which gas is introduced into the combustion chamber for combustion.

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