KR20020067628A - A seven-cylindered, two-stroke crosshead engine with a shaft system - Google Patents

Abstract

PURPOSE: Two-stroke and seven cylinders cross head engine with a shaft system is provided to the measure to prevent torsional oscillation in a shaft device provided with a crankshaft directly connected to a propeller of a ship through at least one propeller shaft of the two-stroke and seven cylinders cross head engine. CONSTITUTION: Two-stroke and seven cylinders cross head engine with a shaft system includes natural frequency of the shaft device to the two-node(k) torsional oscillation mode is within the range of 8.5xMCR(Maximum Continuous Rating) to 12.0xMCR, when MCR is rpm of an engine in the full engine load. When seven cylinders are numbered from a front edge or a back edge, ignition angles(alpha 1-alpha 7) of the cylinders C1-C7 are respectively within ranges of 358 deg. to 2 deg., 105.9 deg. to 109.9 deg., 255.1 deg. to 259.1 deg., 211.7 deg. to 215.7 deg., 155.3 deg. to 159.3 deg., 314.6 deg. to 318.6 deg., and 57.4 deg. to 61.4 deg..

Description

7-cylinder two-stroke crosshead engine with shaft system {A SEVEN-CYLINDERED, TWO-STROKE CROSSHEAD ENGINE WITH A SHAFT SYSTEM}

The present invention relates to a seven-cylinder two-stroke crosshead engine having a shaft system comprising a crankshaft directly connected to the propeller of a ship via at least one propeller shaft.

The direct connection of the crankshaft and the propeller means that the intermediate shaft connection has no gear and the propeller has the same rpm as the crankshaft. The intermediate shaft connection has a propeller shaft that exits out through a stern tube of the hull and may have one or more intermediate shafts depending on the distance between the engine and the propeller shaft.

The crankshaft of the engine is an essential element of both the shaft system and the engine, but the problem is that the crankshaft suitable for viewing from the side of the engine is not compatible with the design suitable for viewing from the side of the shaft system. In a seven-cylinder two-stroke propulsion engine, the problem is that in particular, the engine prefers crankshafts with relatively small masses, but shaft systems typically require crankshafts with relatively large masses of inertia.

It is an object of the present invention to provide a new solution to such a typical problem.

1 shows a crosshead engine according to the invention.

2 is a schematic diagram of a two-node torsional vibration mode.

3 is a diagram showing one embodiment of an ignition angle for the engine of FIG.

In view of the above object, the engine according to the invention is characterized in that the natural frequency of the shaft system for the two-node torsional vibration mode is in the range of 8.5 to 12.0 × MCR, the MCR (maximum continuous rated output; maximum) continuous rating) is the rpm of the engine at full load of the engine.

For a particular engine size, engine MCR is critical to the power provided by the engine, which is also known at an early stage of engine design depending on the case for the cylinder bore, the stroke of the cylinder and the average pressure of the cylinder. The design of the shaft system with natural frequency for the two-node torsional vibration mode in this range gives the shaft system a relatively low torsional rigidity compared to its mass, which makes the crankshaft made of a higher strength material, Make sure you have a smaller mass.

Using a higher strength shaft material means that the stress level of the material can be higher, and also means that a shaft with a smaller cross sectional area and therefore a smaller mass can be produced for a constant load. . The reduced cross sectional area means that the torsional rigidity of the shaft is lower. If the natural frequency becomes smaller than 8.5 x MCR, the shaft becomes too weak against torsion.

In the current natural frequency for the two-node torsional vibration mode, the 9th to 11th torsional vibrations can be responsible for the torsional stress of the shaft. In some cases, the cause may not be substantially important for the overall stress level, but in other cases the stress may be greater than desired, especially in the case of the main bearing journal. In the latter case, correction can be made by adjusting the ignition angle of the engine so that the sum of the causes of the torsional vibration, which changes up to the eleventh vibration, is reduced. In such an embodiment, the ignition angles α1-α7 of the cylinders C1-C7 are 358-2 °, 105.9-109.9 °, 255.1-259.1 °, 211.7-215.7 °, 155.3-159.3 °, 314.6-318.6, respectively. Located in the range of ° and 57.4-61.4 °, the seven cylinders are numbered from the leading or rear end, with the most suitable firing angles being 0 ° for C1, 107.9 ° for C2, 257.1 ° for C3, and C4 for 213.7 ° for C15, 157.3 ° for C5, 316.6 ° for C6 and 59.4 ° for C7.

Embodiments of the engine according to the invention will now be described in more detail with reference to the schematic accompanying drawings.

1 shows, for example, a diesel seven-cylinder crosshead engine 1 fueled with oil and / or gas. The structure of such an engine is well known and it may be, for example, applicant's MC type. The cylinder bore may, for example, be in the range of 35 to 110 cm, the stroke may be in the range of 80 to 400 cm, for example, and the average pressure may be, for example, 18 to 21 bar ( bar), and the output per cylinder may, for example, range from 400 to 7000 kW or more. The engine is a tandem engine with seven cylinders.

The shaft system of the engine is assembled with a crankshaft 2 directly connected to a propeller shaft 3 with a propeller 4, which propeller 4 is directly connected to the propeller shaft or at least one intermediate as desired. It is connected via the shaft 5. If desired, a clutch can be further inserted between the crankshaft and the propeller shaft. When the propeller is of a CP type having a variable pitch, an oil supply shaft may be disposed between the crankshaft and the propeller shaft, and through the oil supply shaft, hydraulic fluid may be supplied to the propeller shaft or to adjust the pitch. It can be passed from the propeller shaft. Optionally, the propeller may be of FP type with a fixed pitch.

2 shows one example of a two-node torsional vibration mode. C1-C7 shows the position of the cylinder in the engine, and P represents the position of the propeller 4. The graph (d) shown shows the relative torsional deflection of the shaft, in which the vibration mode, ie the actual deflection at that axial position, is divided by the maximum torsional deflection of the shaft. The intersection k between the graph d and the horizontal axis gives the position of the node of the torsional vibration. It is evident that the graph d only applies to one particular embodiment, and that the design of the shaft system is positive for the course of the graph and the position of the nodes.

The shaft system has a natural frequency for a two-node torsional vibration mode of n = 1210 cpm. Its natural frequency is determined in a known manner depending on the ratio between the stiffness and the mass of the shaft system. The engine is a 7L60MC with an output of 9840 kW and an average pressure of 14 bar at MCR = 107 rpm. The bore of the engine is 600 mm and the stroke is 1944 mm. If installed on a ship, the MCR can be reduced to 101 rpm without requiring a change to the shaft system if it is desired to change the engine to run at full speed at lower rpm to reduce fuel consumption. If one wants to change the engine to run at full rpm at full rpm to have a higher power, the MCR can vary up to 123 rpm, which is the structurally determined upper limit for that engine.

The crankshaft is made of steel with a tensile strength σ _0.2 of 610 N / mm 2, and the upper limit of nominal stress acceptable in the main bearing journal due to torsional vibration is 30 N / mm 2. The shaft system has a torsional flexibility of about 37 nrad / Nm.

If the variable torsional vibration is undesirably large, there is a possibility of reducing the stress. The stress level is a function of the magnitude of the vibration load and the dynamic state of the vibration system, the vibration load being dependent on the output of the cylinder, the dynamic state of the vibration system being dependent on the engine rpm and the mass-elastic system and the so-called vector sum, The vector sum is determined by the timing of the vibration load in the engine's cycle, which is more specifically determined by the ignition angle of the cylinders.

Since the engine has a constant output and the crankshaft is preferably unaffected by the vibrational state as much as possible, it is desirable that changes in the magnitude of the vibration-elastic system and the vibration load are avoided.

Looking at the vector sum, the contribution of vibration to the two-node torsional vibration mode consists of the contribution of the torque that changes over time from each cylinder. In a well known manner, the contribution of this vibration can be decomposed into harmonic components, and for each of its orders i, there is a circulating resonance number (ω _i = n / i), where The order resonates with the natural frequency of the shaft system. Since the ship's propulsion engine generally operates sufficiently continuously at its MCR, it is particularly appropriate to consider a harmonic component that can have resonance at rpm close to the MCR. Due to the natural frequency for the two-node torsional vibration mode in the range of 8.5 to 12.0 x MCR, vibrations of the ninth through twelfth order may be considered.

Such consideration may begin with an ignition angle equivalent to the ignition sequence of C1 C7 C2 C5 C4 C4 C3 C6, ie a 7-cylinder engine of the MC type with a rotation angle of 360/7 ° = 51.4 ° between each ignition. . On this basis an ignition angle is calculated which results in a lower vector sum for vibrations of ninth through twelfth orders.

In Fig. 3, a particularly advantageous set of ignition angles is 0 ° for C1, 107.9 ° for C2, 257.1 ° for C3, 213.7 ° for C4, 157.3 ° for C5, 316.6 ° for C6 and C7 Presented at 59.4 °. These ignition angles are substantially smaller for the 9th to 12th order vibrations without significant change in the negative direction of the free forces and other vibration parameters such as the primary and secondary moments, the guiding force of the shaft system or the axial vibrations. Present the vector sum. These ignition angles are torsional vibrations despite the fact that the ninth, tenth, eleventh and twelfth torsional vibrations are selected to have their natural frequencies at or near the point of continuous operation of the engine. It is possible to manufacture a shaft system without an actuating member for damping the pressure. The ignition angle can vary within an angle difference of up to 2 degrees. Other sets of ignition angles are also possible to make an advantageous small contribution to the 9th to 12th torsional vibrations.

Another embodiment of a seven-cylinder engine, which can advantageously apply the ignition angles mentioned in claims 2 and 3, is an engine 7K80MC-C having a power of 21280 kW at an MCR of 97 rpm. Engine 7K98MC-C with a maximum power of 39970 kW at an MCR of rpm, and other sized engines with bores of 900 mm, 840 mm, 700 mm, 500 mm and 460 mm, for example.

The ignition angles provide a somewhat uneven ignition sequence in which crankshaft rotations of 59.4 °, 48.5 °, 49.4 °, 56.4 °, 43.4 °, 59.5 °, and 43.4 ° occur between each ignition.

If the natural frequency of the shaft system is substantially larger than 12 × MCR, the desired action is too insufficient, and furthermore, 13 or more orders of magnitude of vibration may occur.

According to the present invention, a seven-cylinder two-stroke propulsion engine with a relatively small mass crankshaft can be provided.

Claims (3)

In a seven-cylinder two-stroke crosshead engine 1 having a shaft system comprising a crankshaft 2 directly connected to the ship's propeller 4 via at least one propeller shaft 3, a two-node k 7) The natural frequency of the shaft system for torsional vibration mode is in the range of 8.5 to 12.0 x MCR, wherein the MCR is the rpm of the engine at full load of the engine. The ignition angles α1-α7 of the cylinders C1-C7 are respectively 358-2 °, 105.9-109.9 °, 255.1-259.1 °, 211.7-215.7 °, 155.3-159.3 ° and 314.6-. 7-cylinder two-stroke crosshead engine in the range of 318.6 ° and 57.4-61.4 °, wherein the number of seven cylinders is designated from the leading or rear end of the engine. The ignition angle of claim 2, wherein the firing angle is 0 ° for C1, 107.9 ° for C2, 257.1 ° for C3, 213.7 ° for C4, 157.3 ° for C5, 316.6 ° for C6 and 59.4 for C7. A 7-cylinder two-stroke crosshead engine characterized by °.