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System reliability design refers to the optimal design of the system under the premise of meeting the specified reliability indicators and expected functions, so that the technical performance of the system and the subsystems are coordinated with each other. The reliability design of the ship system is generally the reliability distribution. It assigns the system reliability index specified in the design task book to the subsystem unit of the system reasonably, as an important parameter of the unit design, and predicts the system through reliability distribution. The weak link, which improves the reliability of the entire system and achieves optimal design. Among them, the shafting, diesel engine and base have the greatest impact on the reliability of marine gear transmission. Therefore, it is necessary to reasonably distribute the reliability of adjacent subsystems of the gear transmission.
The influence of the shafting on the gear transmission The ship is a flexible body, and the elastic shaft system changes the position of the axis with the working environment and conditions, which affects the life of the gear. When the ship is continuously sailing, under the action of the load on the shafting, the additional bending moment, the torque and the displacement, the gear shaft sways and tilts away from the steady position of the bearing, causing the two axes of the transmission gear to be non-parallel, so that the load along the Uneven distribution and concentration of the tooth width lead to fatigue damage of the gear teeth. Especially for large torque propellers and large shaft shaft propulsion systems, because of the large gears that transmit power, they are subjected to a pair of equal-sized and opposite-direction pinion loads on the same horizontal plane. The inclination and deformation of the shaft system will cause the supporting gears. The large changes in bearing load magnitude and direction exacerbate bearing wear and failure.
Misalignment of the axis will cause unbalanced forces and vibrations, but excessive radial compensation also produces a reaction force that causes overloading of the bearing and deformation of the pinion shaft. The influence of the base on the gear transmission The frame of the ship machinery is usually an unstable and elastic platform. When the gear box supports the foot and the machine base is in a rigid contact with multiple points, and the gear box is forced to be randomly seated. And the propeller thrust is directly transmitted to the gear box through the ship structure, causing poor contact and tooth breaking of the gear tooth surface. Reliability method: elastic coupling and floating structure Install a high-elastic coupling with damping characteristics between the input shaft of the diesel engine and the gear transmission. On the one hand, due to the good elasticity and damping effect of the coupling, the resonance system is self-contained. The vibration frequency drops below the working speed, which improves the torsional vibration characteristics of the system and reduces the amplitude of the input shaft. On the other hand, the high-elastic coupling can compensate for the misalignment of the shaft due to hull deformation and installation error. The system has obvious vibration absorption and vibration damping effects.
At the same time, the input shaft of the transmission adopts a floating support structure. The input shaft is arranged separately from the pinion shaft and has no bearing support inside. The front end of the input shaft is coupled to the diesel engine by a high-elastic coupling, which has radial, axial and angular compensation functions; and the rear end is rigid with the active portion of the multi-disc clutch by the hollow pinion. Therefore, either end of the input shaft has a floating characteristic, which can compensate for various displacements and solve the alignment problem of the installation. The symmetrical design and the independent support apply the symmetry principle to design the gear reducer, and the main components of the box, gear, shaft and bearing are symmetrically arranged. In order to maintain symmetry, the thrust bearing is mounted separately from the gearbox, independent of the housing. The gearbox base support is designed as a three- or four-point resilient support structure that is symmetrically arranged along the axis. The shape of the gearbox is designed to increase the rigidity of the box, reduce the area of ​​the bearing surface of the base, and increase the distance between the input shaft end and the fulcrum. The structure of the base 25 is independent and independent of each other. It is installed on the hull of the hull. The axis of the gearbox coincides with the longitudinal gird of the hull. Even if the single base is deformed, it will not affect the deformation of other bases and gearbox. At the same time, the base 1 of the thrust bearing is arranged separately from the gear box base 25, and the deformation caused by the axial thrust of the propeller is prevented from being directly transmitted to the gear box. Therefore, the independent support structure makes the hull deformation, the propeller thrust and the gear box completely isolated, ensuring the parallelism and transmission reliability of the two-axis system. Adjusting the height and moderate alignment improves the alignment of the shafting and the accuracy of the installation is beneficial to improve the vibration environment of the system, but moderate alignment will improve the stress state of the gear transmission bearing.
Under the action of the meshing force and gravity, the large gears of the gear transmission sometimes have a large difference in the radial force of the two bearings, and the unbalanced bearing force accelerates the wear and affects the working life. If the height position of the first support bearing of the intermediate shaft in the shafting is moderately adjusted, the bearing force of the gear transmission can be greatly improved. In order to force the middle shaft system, if the gear is subjected to a force of 150 kN, the force difference between the two bearing bearings is 40 kN, and the force of the intermediate bearing is 10 kN. The test shows that the moderate centering increases the bearing life by more than 60. The reliability of marine gearing is closely related to its neighboring subsystems. Elastic coupling, floating structure, symmetrical design, independent support and moderate alignment significantly improve the working life and reliability of the gearing system. According to the degree of influence of each subsystem on the reliability of gear transmission and its importance, rationally assigning the reliability of each unit is an effective way to improve the reliability of the transmission system.