JP4156247B2 - 2-stroke crosshead engine with 7 cylinders - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a two-stroke crosshead engine with seven cylinders having a shaft device comprising a crankshaft directly connected to a ship propeller via at least one propeller shaft.
[0002]
[Prior art]
Connecting the crankshaft and the propeller directly means that the intermediate shaft connecting portion does not have any gear, and the propeller has the same rpm as the crankshaft. The intermediate shaft connection has one propeller shaft that penetrates the hull stern tube and possibly one or more intermediate shafts, depending on the distance between the engine and the propeller shaft. ing.
[0003]
The crankshaft of the engine is an essential element of both the shaft device and the engine, but one problem is that the design of the crankshaft that is preferable from the engine side conflicts with the preferable design from the viewpoint of the shaft device. In a two stroke propulsion engine with seven cylinders, the engine prefers a relatively low mass crankshaft, while the shaft system conventionally requires a crankshaft with a relatively large mass moment of inertia, so this problem is Especially noticeable.
[0004]
One object of the present invention is to provide a novel solution to this classic problem.
[0005]
In view of this, the engine according to the present invention has an MCR of 8 when the natural frequency of the shaft device for the two-node torsional vibration mode is MCR (maximum continuous rating value) at full engine load and engine rpm. It is characterized by being in the range of 5 times to 12.0 times.
[0006]
For any particular engine size, the engine's MCR is critical to the power provided by the engine and, as is the case with cylinder bore, cylinder stroke distance and average pressure, during the early stages of engine design. Known. The design of the shaft device having a natural frequency within the above range for the two-bar torsional vibration mode provides a shaft device having a relatively small torsional stiffness compared to its mass, and this further improves the shaft device. Manufactured from a high strength material and allows the shaft device to have a smaller mass.
[0007]
[Problems to be solved by the invention]
Using a higher-strength shaft material results in a higher material stress level, and for constant loads, the shaft can be formed with a smaller cross-sectional area, thereby forming a higher mass. Means you can. A reduced cross-sectional area means that the torsional stiffness of the shaft is reduced. If the natural frequency is 8.5 × MCR or less, the shaft becomes excessively flexible in terms of torsion.
[0008]
[Means for Solving the Problems]
In the case of the current natural frequency for a two-node torsional vibration, the ninth to eleventh order torsional vibrations may contribute to the torsional stress of the shaft. In some cases, this contribution is not substantially important to the overall stress level, while in other cases, particularly in the main bearing journal, the stress can be greater than desired. This latter case can be compensated by adjusting the ignition angle of the engine so that the degree to which the total value of the contribution ratio of the torsional vibration to the eleventh-order vibration changes is reduced. In this embodiment, if seven cylinders are numbered from the front end or the rear end of the engine, the ignition angles (α1 to α7) of the cylinders C1 to C7 are 358 ° to 2 ° and 105.9, respectively. ° to 109.9 °, 255.1 ° to 259.1 °, 211.7 ° to 215.7 °, 155.3 ° to 159.3 °, 314.6 ° to 318.6 ° and 57.4 And most preferably, the ignition angle for the cylinder C1 is 0 °, the ignition angle for the cylinder C2 is 107.9 °, the ignition angle for the cylinder C3 is 257.1 °, and the ignition for the cylinder C4 The angle is 213.7 °, the ignition angle for the cylinder C5 is 157.3 °, the ignition angle for the cylinder C6 is 316.6 °, and the ignition angle for the cylinder C7 is 59.4 °. To so that.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the engine according to the invention will now be described in more detail with reference to the very schematic drawings.
[0010]
FIG. 1 shows, for example, a diesel-type seven-cylinder crosshead engine 1 using oil and / or gas as fuel. The structure of such an engine is well known and can be, for example, the model MC of the applicant. The cylinder bore is, for example, in the range of 35 to 110 cm, the stroke distance is in the range of, for example, 80 cm to 400 cm, the average pressure is, for example, in the range of 1800 kPa (18 bar) to 2100 kPa (21 bar), and the output per cylinder Can be in the range of 400 kW to 7000 kW or more, for example. This engine is an inline engine having seven cylinders.
[0011]
The engine shaft device comprises a crankshaft 2 connected directly to the propeller shaft 3 together with the propeller 4, either directly to the propeller shaft or in a manner via at least one intermediate shaft 5, as desired. It is formed by. If desired, a clutch may be further inserted between the crankshaft and the propeller shaft. If the propeller is of the variable pitch CP type, there is an oil distribution shaft between the crankshaft and the propeller shaft, through which the hydraulic fluid is passed to the propeller or to the propeller to adjust its pitch. Can be passed through. Alternatively, the propeller may be an FP type with a constant pitch.
[0012]
FIG. 2 shows an example of a two-node torsional vibration mode. C1 to C7 indicate the positions of the cylinders in the engine, while P indicates the position of the propeller 4. The illustrated graph d shows the relative torsional deflection of the shaft in the vibration mode, that is, the value obtained by dividing the actual deflection in the axial direction by the maximum torsional deflection of the shaft. The intersection point k between the graph d and the horizontal axis indicates the position of the node of torsional vibration. It is clear that the graph d applies only to one specific embodiment, and that the design of the shaft device affects the trajectory of the graph and the position of the nodes.
[0013]
The shaft device has a natural frequency for the two-node torsional vibration mode when n = 1210 cpm. This natural frequency is determined in a known manner by the ratio between the stiffness of the shaft device and its mass. This engine is 7L60MC with an output of 9840 kW at MCR = 107 rpm and an average pressure of 1400 kPa (14 bar). The engine bore is 600 mm and the stroke distance is 1944 mm. If it is desirable to change the engine to operate at full load at a lower rpm so that the specific fuel consumption can be reduced after installation on a ship, without requiring changes to the shaft system, If it is desired to reduce the MCR to 101 rpm and it is desirable to change the engine to operate at full load at higher rpm for higher output, it is structurally determined for that engine. The MCR can be changed to the upper limit of 123 rpm.
[0014]
The crankshaft is made of steel with a tensile strength σ _0.2 of 610 N / mm ² and the upper limit of the allowable nominal stress in the main bearing journal as a result of torsional vibration is 30 N / mm ² . The shaft device has a torsional flexibility of about 37 nrad / Nm.
[0015]
If the change in torsional vibration is undesirably large, there are several possible ways to reduce the stress. The stress level is a function of the magnitude of the excitation force depending on the output of the cylinder, depends on the mass elastic system and the engine rpm, and depending on when the excitation force acts during the engine cycle, It is a function of the dynamic state of the vibration device depending on the so-called vector sum determined more specifically by the ignition angle of the cylinder.
[0016]
Since it is desirable for the engine to have a specific output and as much as possible the crankshaft is not affected by vibration conditions, it is preferable to avoid changes to the mass-elastic system and changes in the magnitude of the excitation force.
[0017]
With respect to the vector sum, the vibration contribution to the two-bar torsional vibration mode consists of individual cylinder torque contributions that vary with time. In a well-known manner, these vibration contributions can be decomposed into harmonic components, and for each i-th order there is a resonance rotational speed ω _i = n / i, at which point the vibration order Resonates with the natural frequency of the shaft device. Since a ship's propulsion engine typically operates continuously primarily at its MCR, it is particularly reasonable to consider harmonic components that resonate at rpm near the MCR. When the natural frequency for the two-node torsional vibration mode is in the range of 8.5 × MCR to 12.0 × MCR, vibrations of the ninth order to the twelfth order can be considered.
[0018]
In this examination, the ignition order (ignition order) is cylinders C1, C7, C2, C5, C4, C3, C6, and the ignition angles are equal, that is, the rotation angle between each ignition is 360/7 ° = 51.4. It can start with an engine with MC 7 cylinders. Based on this, the ignition angle at which the vector total value for the vibrations of the ninth order to the twelfth order becomes small is calculated.
[0019]
A particularly advantageous ignition angle combination is illustrated in FIG. 3, which is 0 ° for cylinder C1, 107.9 ° for cylinder C2, 257.1 ° for cylinder C3, 213.7 ° for cylinder C4, 157.3 ° for cylinder C5, 316.6 ° for cylinder C6, and 59.4 ° for cylinder C7. These ignition angles have a remarkably small vector sum for vibrations of the ninth to twelfth orders, and are like the free force of the shaft device, the first and second order moments, the guide force or the vibration in the axial direction. The other vibration parameters are not significantly changed in the direction of invalidation. The natural frequency of the shaft device is selected so that the ninth order, tenth order, eleventh order and twelfth order torsional vibrations have their resonance points in the vicinity of the point where the engine operates continuously. Nevertheless, these ignition angles make it possible to manufacture the shaft device without the need for an actable member to dampen torsional vibrations. These ignition angles can be changed within an angle range of 2 ° or less. Other sets of ignition angles are possible so that an advantageous small contribution to the ninth to twelfth order torsional vibrations can be realized.
[0020]
Other examples of a 7-cylinder engine that can advantageously apply the ignition angle according to claim 2 and claim 3 are an engine 7K80MC-C with an output of 21280 kW when the MCR is 97 rpm, and an MR when the MCR is 104 rpm 7K98MC-C with a maximum output of 39970 kW, for example, other engine sizes with bores of 900 mm, 840 mm, 700 mm, 500 mm and 460 mm.
[0021]
The ignition angles described above provide a slightly non-uniform ignition order, in which case the crankshaft rotation between individual ignitions is 59.4 °, 48.5 °, 49.4 °, 56.4 °, respectively. , 43.4 °, 59.5 ° and 43.4 °.
[0022]
If the natural frequency of the shaft device is significantly greater than 12 * MCR, the desired effect will be too inadequate, and vibration contributions may result from thirteenth or higher order vibrations.
[Brief description of the drawings]
FIG. 1 is a diagram of a crosshead engine according to the present invention.
FIG. 2 is an external view of a two-bar torsional vibration mode.
FIG. 3 is a diagram showing an example of an ignition angle of the engine of FIG. 1;
[Explanation of symbols]
1 Crosshead engine with 7 cylinders 2 Crankshaft 3 Propeller shaft 4 Propeller 5 Intermediate shaft

Claims (2)

In a two-stroke crosshead engine (1) with seven cylinders having a shaft arrangement comprising a crankshaft (2) connected directly to the ship propeller (4) via at least one propeller shaft (3),
When seven cylinders are numbered from the front end or the rear end of the engine when the crankshaft cross section is viewed from the end having the crank arm at 0 ° in the vertical direction, the cylinders C1 to C7 The ignition angles (α1 to α7) are 358 ° to 2 °, 105.9 ° to 109.9 °, 255.1 ° to 259.1 °, 211.7 ° to 215.7 °, 155.3 °, respectively. The natural vibration of the shaft device for the two-node (k) torsional vibration mode by being in the range of 159.3 °, 314.6 ° to 318.6 ° and 57.4 ° to 61.4 ° The number is within the range of 8.5 × MCR to 12.0 × MCR (where MCR is the engine speed (rpm) at the maximum engine load at the maximum continuous rated value). Features a crankshaft To, 7 two-stroke crosshead engine with a cylinder. A two-stroke crosshead engine with 7 cylinders according to claim 1,
  0 ° for cylinder C1, 107.9 ° for cylinder C2, 257.1 ° for cylinder C3, 213.7 ° for cylinder C4, 157.3 ° for cylinder C5, 316.6 for cylinder C6 2 stroke crosshead engine with 7 cylinders, characterized in that the ignition angle is 59.4 ° with respect to the cylinder C7.

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