JPS648225B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a device for preventing longitudinal vibration of a rotating shaft, and more specifically, it relates to a device for preventing longitudinal vibration of a propulsion shaft system of a ship, etc. and a ship hull induced by it. The present invention relates to a device for effectively preventing local vibrations.

[Prior art] Longitudinal vibrations in a ship's propulsion shaft system are caused by the excitation force of the propeller, and when the main engine is a diesel,
Some are based on the combustion gas pressure of the engine. The former occurs because the propeller blades rotate in the non-uniform wake at the stern, and the main component of the excitation force has a frequency equal to the propeller shaft rotation speed multiplied by the propeller blade number. In addition, in the latter case, torque fluctuations in the combustion gas pressure of the engine are accompanied by fluctuations in the propeller rotation, which is converted into fluctuations in the propeller thrust and becomes an excitation force for longitudinal vibration of the shaft system, and the same torque fluctuation is caused by the engine's Some systems use a crankshaft mechanism to directly induce longitudinal vibration of the crankshaft. The frequency of the main component of the excitation force based on the combustion gas pressure of these engines is commonly used in large marine diesel engines. For a two-stroke engine, it is equal to the crankshaft speed multiplied by the number of cylinders.

[Problems to be Solved by the Invention] However, the above-mentioned longitudinal vibration of the propulsion shaft system itself causes wear of the stern tube, loosening of the thrust bearing stand, damage to the crankshaft, etc., and also causes damage to the thrust bearing. This is transmitted to the ship's hull through the engine mount, causing longitudinal vibrations of the entire engine mount and local vibrations of the superstructure, which can cause problems. In particular, as engines with high horsepower and a small number of cylinders have recently come into use for the purpose of energy conservation, the occurrence of these vibration problems has become more noticeable.

Therefore, in order to avoid resonance of the propulsion shaft system due to the above-mentioned vibrational force, it is necessary to sufficiently increase the longitudinal and torsional rigidity of the shaft system in advance, and if local vibrations occur on the hull side, it is necessary to The main approach was to take passive measures such as reinforcing the structure.

The present invention has been made to solve the above problems, and provides a longitudinal vibration prevention device for a rotating shaft that can automatically and effectively prevent longitudinal vibration of the rotating shaft over the entire rotation range. .

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a rotary shaft that rotates together with the rotary shaft and is vibrating in the direction of the rotary shaft about a pendulum fulcrum located away from the center of the rotary shaft. A plurality of centrifugal pendulums are provided axially symmetrically, and the pendulum length from the center of gravity of these centrifugal pendulums to the pendulum fulcrum and the distance from the center of gravity to the center of the rotation axis are such that the natural frequency of the pendulum is vertical to the rotation axis. The vertical vibration of the rotary shaft is set to match the frequency of the vibration, and the centrifugal pendulum vibrates in synchronization with the vertical vibration of the rotating shaft.

[Operation] First, the principle of a dynamic vibration absorber will be described. As is well known, this principle is based on the fact that when a main vibration system vibrating under a steady excitation force is added with another small vibration system having a natural frequency equal to the frequency of the vibration excitation force,
The principle is that this small vibration system vibrates in synchrony with the excitation force, and the vibration inertia balances and cancels out the excitation force of the main vibration system, so the main vibration system is kept in a stationary state. A device that absorbs the vibration of the main vibration system through its own tuned vibration, such as the additional small vibration system in this case, and has a damping effect, is called a dynamic vibration reducer.

By the way, since a normal dynamic vibration absorber is basically formed of a mass-spring system, its natural frequency remains unchanged during operation. Therefore, if the excitation force frequency of the main vibration system changes over a wide range, the dynamic vibration absorber will have no effect at all, except in specific cases where the excitation force frequency happens to match the natural frequency of the dynamic vibration absorber. It is not demonstrated.

Generally, the frequency of the excitation force acting on a vibration system is proportional to the rotation speed of the rotating body that is the source of the vibration, so if the natural frequency of the dynamic vibration absorber is set to the rotation speed of the source of the vibration force, If it can be made proportional, it will be possible to always match the natural frequency of the dynamic vibration absorber to the frequency of the excitation force, which will result in an ideal dynamic vibration absorber that can keep the main vibration system stationary throughout the entire rotation speed. That's why. Such an ideal dynamic vibration absorber can be realized by using a centrifugal pendulum.

A centrifugal pendulum is a pendulum that vibrates in a field where centrifugal force acts instead of gravity in a normal pendulum, and this will be explained with reference to FIGS. 1 and 2. Figure 1 shows a weight C attached to a rotating shaft A via a hanging B.
An example of a single pendulum-type centrifugal pendulum P is shown. This pendulum P can vibrate only in the direction of the rotation axis while rotating together with the rotation axis A. In the figure, O represents the center of the rotation axis, H represents the fulcrum of the pendulum, and G represents the center of gravity of the pendulum. Now, the length of the pendulum P from the center of gravity G of the pendulum to the pendulum fulcrum H is l, the distance from the center of gravity G of the pendulum to the center of rotation O is s, the mass of the pendulum P is m,
If the angular velocity of the rotation axis A is ω, then the centrifugal force F acting on the pendulum center of gravity G is msω ^2. Therefore, the natural frequency f of the centrifugal force pendulum P is expressed by the following equation in the small amplitude range. be done.

However, n is the number of rotations of rotation axis A, and n = ω/2π
It is.

Figure 2 shows a floating circular centrifugal pendulum P on the rotation axis A.
An example is shown in which the is installed. In this case, from the connecting point Q of the two hangings B and B's pendulum P of equal length to the hanging fulcrum.
Since the length l to H′ is the pendulum length of the pendulum P,
The pendulum fulcrum H is a point located from the center of gravity of the pendulum by l from G to the center of rotation axis O. The natural frequency of the pendulum P in this case is also given by equation (1).

As can be seen from equation (1), the natural frequency f of the centrifugal pendulum is proportional to the rotational speed n of the rotating shaft A to which it is attached. Therefore, by appropriately selecting the values of s and l of the pendulum, the ratio of f and n can be chosen to any desired value.

When the centrifugal force pendulum P described above is installed at an appropriate location on the propulsion shaft system of a ship, for example, an intermediate shaft (a shaft between the main engine crankshaft and the propeller shaft) as a dynamic vibration absorber that targets the excitation force of the propeller. As mentioned above, the frequency of the main component of the excitation force is 4n when there are four propeller blades, so in equation (1), f
=4n, then S/l=4 ² =16...(2). Therefore, if the center of gravity of the pendulum and the length of the pendulum are determined to satisfy this equation, the excitation force of the propeller will be canceled out by the inertial force of the centrifugal pendulum P, and the longitudinal vibration of the intermediate shaft will be offset by the centrifugal pendulum P. will be absorbed into.

In addition, when considering the excitation force due to the combustion gas pressure of a diesel engine, the frequency of the main component of the excitation force is, for example, 5n in the case of a 5-cylinder engine, so f = 5n, the following relational expression is obtained: S/l=5 ² =25...(3). Therefore, the center of gravity position of the pendulum and the length of the pendulum in this case can be determined using equation (3).

Therefore, since the weight of the centrifugal pendulum is easily determined from the condition that the inertial force due to the vibration of the pendulum and the excitation force are balanced, the shape, size, number, and arrangement of the pendulum are determined, and the dynamic vibration absorber The design will be carried out.

[Embodiment] A preferred embodiment of the present invention will be described based on the accompanying drawings.

3 and 4 show a centrifugal pendulum installed on the intermediate shaft of an actual ship equipped with a 5-cylinder diesel engine in order to prevent longitudinal vibrations occurring in the propulsion shaft system. FIG. 3 is a side view, and FIG. 4 is a sectional view taken along the line -- in FIG. Moreover, FIG. 5 is an enlarged view of the pendulum main body portion of FIG. 3. In the figure, 1 is an intermediate shaft of the propulsion shaft system, 2 is a support for attaching a centrifugal force pendulum as a dynamic vibration absorber to the intermediate shaft 1, and 3 is a support radially outward at 90° intervals from the support 2. A pendulum support plate is formed in an overhanging manner, and 4 is a bifurcated end 3a at the tip of the pendulum support plate 3.
It is attached to the pendulum support plate 3 through rolling rollers 5 which are freely supported in roller receiving holes 6 formed at equal distances from the intermediate shaft 1, and whose longitudinal direction is in the axial direction of the intermediate shaft 1. A rectangular parallelepiped pendulum body is arranged along the pendulum body, 7 is a roller insertion hole provided in two places in the pendulum body 4 opposite to the roller receiving hole 6 on the pendulum support plate 3 side, and 8 is a roller insertion hole on the pendulum support plate 3 side. A blind cover 9 closes the roller receiving hole 6, and 9 indicates a bolt and nut for tightening the two semi-cylindrical members constituting the support base 2 to the intermediate shaft 1.

The blind lids 8, which are attached to both sides of the forked ends 3a of the pendulum support plate 3 and which close the roller receiving holes 6, are designed to prevent the rolling rollers 5 from falling off and to prevent the rollers from being worn out. This is to preserve the grease filled inside the lid 8.

When the intermediate shaft 1 is rotating, the pendulum body 4 is moved radially outward by centrifugal force and positioned as shown in the figure. At that time, the rolling rollers 5
By rolling on the inner surfaces of the opposing roller receiving holes 6 and roller insertion holes 7 on the pendulum main body 4 side, the pendulum main body 4 is in a state where it can vibrate in the axial direction of the intermediate shaft 1 in a floating circular manner. As mentioned above, the pendulum length l of the pendulum movement in this case corresponds to the length from the connection point Q of the pendulum P to the hanging fulcrum H' shown in FIG. The center of corresponds to the hanging fulcrum H', and the center of the roller insertion hole 7 corresponds to Q. Therefore, if the diameter of the roller receiving hole 6 and the roller insertion hole 7 is D, and the diameter of the rolling roller 5 is d, then the rolling roller 5 exists between the roller receiving hole 6 and the roller insertion hole 7. Therefore, the pendulum length l is given by l=D−d, and the pendulum fulcrum H with respect to the center of gravity G of the pendulum body 4
is given, this l and the center of gravity G of the pendulum body 4
If the distance s from to the rotational axis center O is selected according to the relationship of equation (3) above, the natural frequency f of this pendulum when the intermediate shaft 1 is rotating at the rotational speed n
As mentioned above, f = 5n, so the excitation force of the longitudinal vibration of the propulsion shaft system with a frequency of 5n is absorbed by the vibration of the pendulum throughout the entire rotation speed, and the vibration of the propulsion shaft system As mentioned above, the longitudinal vibration of will disappear.

Figures 3 and 4 only show a centrifugal pendulum that targets the excitation force from the engine, but if you want to absorb the excitation force of the propeller (due to uneven wake at the stern), Similarly, in the middle of the pendulum shown
Another four centrifugal pendulums may be arranged at 90° intervals. Of course, in that case, when there are four propeller blades, the center of gravity position and pendulum length of the pendulum are determined according to the relationship in equation (2) above, and the weight of the pendulum is determined by the magnitude of the propeller excitation force. must be decided accordingly.

In addition, in the centrifugal pendulum of the mechanism shown in Figs. 3 and 4, the motion of the rolling roller 5 affects the natural frequency of the pendulum, but the amount of correction is small and can be calculated accurately. So there is no problem. Furthermore, when the rotation axis is stationary, centrifugal force does not work, so the pendulum body 4 located at an angle other than perpendicularly downward to the rotation axis will not take the position shown in the figure due to the pull of gravity. However, once rotation begins, the centrifugal force acting on the pendulum generally far exceeds gravity (for example,
In the example calculation shown in this figure, the centrifugal force is 14 times the gravity), so there is no need to worry about the influence of gravity.

[Effects of the Invention] As is clear from the above description, the present invention can exhibit the following excellent effects.

(1) The vibration absorption effect by the device of the present invention is performed completely automatically over the entire rotation of the rotating shaft such as the propulsion shaft system during normal operation, and also follows fluctuations in the rotation speed. Very large.

(2) Since the structure of the device is simple, it can be manufactured at low cost.

(3) When installed on the intermediate shaft of a ship's propulsion shaft system,
It can be easily installed using the small space around the intermediate shaft.

(4) Tuning of the natural frequency of the centrifugal pendulum and the frequency of the excitation force can be performed extremely accurately using clear calculation formulas and simple preliminary experiments.

(5) By appropriately combining several types of pendulum groups with different shapes, dimensions, and arrangements, it is possible to absorb several types of excitation forces with different frequencies and sizes all at once with one device.

[Brief explanation of drawings]

FIGS. 1 and 2 are diagrams explaining the principle of a centrifugal pendulum, which is the core of the present invention. FIG. 1 shows a case where the pendulum is a single pendulum type, and FIG. 2 shows a case where the pendulum is a floating circular pendulum. Figures 3 and 4 show an embodiment of the device according to the present invention, which is installed on the intermediate shaft of an actual ship equipped with a 5-cylinder low-speed diesel engine, as a longitudinal vibration prevention device for the propulsion shaft system. In the figure, the third
The figure is a side view thereof, FIG. 4 is a sectional view taken along the line -- in FIG. 3, and FIG. 5 is an enlarged view of the pendulum portion in FIG. 3. In the figure, 1 is the intermediate shaft (rotating shaft), 2 is the support base, 3 is the pendulum support plate, 3a is the two-pronged end of the pendulum support plate, 4 is the pendulum body, 5 is the rolling roller, 6 is the roller receiving hole, 7 is a roller insertion hole, 8 is a blind cover of the roller hole 6, and 9 is a bolt/nut for attaching the support base to the intermediate shaft.

Claims (1)

[Claims] 1. A plurality of centrifugal force pendulums are installed in an axially symmetrical manner around a pendulum fulcrum at a position away from the center of the rotational axis while rotating together with the rotational axis, and can vibrate in the direction of the rotational axis. A vertical axis of rotation, characterized in that the length of the pendulum to the fulcrum and the distance from the center of gravity to the center of the rotation axis are set so that the natural frequency of the pendulum matches the frequency of longitudinal vibration of the axis of rotation. Anti-vibration device.